Monday, February 21, 2011

Computer BIOS

In IBM PC Compatible computers, the basic input/output system (BIOS), also known as the System BIOS, is a de facto standard defining a firmware interface.

The BIOS software is built into the PC, and is the first code run by a PC when powered on ('boot firmware') (Dell XPS M1210 Battery) http://www.hdd-shop.co.uk .

The primary function of the BIOS is to load and start an operating system. When the PC starts up, the first job for the BIOS is to initialize and identify system devices such as the video display card, keyboard and mouse, hard disk, CD/DVD drive and other hardware Dell Studio XPS 1640 Battery .

The BIOS then locates software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD, and loads and executes that software, giving it control of the PC. This process is known as booting, or booting up, which is short for bootstrappingDell Vostro 1710 Battery .

BIOS software is stored on a non-volatile ROM chip built into the system on the mother board. The BIOS software is specifically designed to work with the particular type of system in question, including having a knowledge of the workings of various devices that make up the complementary chipset of the system Dell KM958 battery .

In modern computer systems, the BIOS chip's contents can be rewritten allowing BIOS software to be upgraded.

A BIOS will also have a user interface (or UI for short). Typically this is a menu system accessed by pressing a certain key on the keyboard when the PC starts. In the BIOS UI, a user can Dell Studio 1555 battery :

  • configure hardware
  • set the system clock
  • enable or disable system components
  • select which devices are eligible to be a potential boot device Sony VGP-BPS13 battery
  • set various password prompts, such as a password for securing access to the BIOS UI functions itself and preventing malicious users from booting the system from unauthorized peripheral devices Sony VGP-BPS13/B battery .

The BIOS provides a small library of basic input/output functions used to operate and control the peripherals such as the keyboard, text display functions and so forth, and these software library functions are callable by external software Sony VGP-BPS13/S battery .

In the IBM PC and AT, certain peripheral cards such as hard-drive controllers and video display adapters carried their own BIOS extension ROM, which provided additional functionality. Operating systems and executive software, designed to supersede this basic firmware functionality, will provide replacement software interfaces to applications Sony VGP-BPS13A/B battery .

The role of the BIOS has changed over time; today BIOS is a legacy system, superseded by the more complex EFI (EFI), but BIOS remains in widespread use, and EFI booting has only been supported in Microsoft OS products supporting GPT and Linux Kernels 2.6.1 and greater builds Sony VGP-BPS13B/B battery .

BIOS is primarily associated with the 16-bit, 32-bit, and the beginning of the 64-bit architecture eras, while EFI is used for some newer 32-bit and 64-bit architectures. Today BIOS is primarily used for booting a system and for video initialization (in X.org); but otherwise is not used during the ordinary running of a system Sony VGP-BPL9 battery ,

while in early systems (particularly in the 16-bit era), BIOS was used for hardware access – operating systems (notably MS-DOS) would call the BIOS rather than directly accessing the hardware. In the 32-bit era and later, operating systems instead generally directly accessed the hardware using their own device drivers Sony VGP-BPS13B/B battery .

However, the distinction between BIOS and EFI is rarely made in terminology by the average computer user, making BIOS a catch-all term for both systems.

Terminology

The term first appeared in the CP/M operating system, describing the part of CP/M loaded during boot time that interfaced directly with the hardware (CP/M machines usually had only a simple boot loader in their ROM) Sony VGP-BPL15 battery .

Most versions of DOS have a file called "IBMBIO.COM" or "IO.SYS" that is analogous to the CP/M BIOS.

Among other classes of computers, the generic terms boot monitor, boot loader or boot ROM were commonly used. Some Sun and PowerPC-based computers use Open Firmware for this purpose Dell Inspiron E1505 battery .

There are a few alternatives for Legacy BIOS in the x86 world: Extensible Firmware Interface, Open Firmware (used on the OLPC XO-1) and coreboot.

IBM PC-compatible BIOS chips

In principle, the BIOS in ROM was customized to the particular manufacturer's hardware, allowing low-level services (such as reading a keystroke or writing a sector of data to diskette) to be provided in a standardized way to the operating system Dell Latitude E6400 battery .

For example, an IBM PC might have had either a monochrome or a color display adapter, using different display memory addresses and hardware - but the BIOS service to print a character on the screen in text mode would be the same HP Pavilion dv6000 Battery .

Boot Block
DMI Block
Main Block

Prior to the early 1990s, BIOSes were stored in ROM or PROM chips, which could not be altered by users. As its complexity and need for updates grew, and re-programmable parts became more available, BIOS firmware was most commonly stored on EEPROM or flash memory devices SONY VAIO VGN-FZ Battery .

According to Robert Braver, the president of the BIOS manufacturer Micro Firmware, Flash BIOS chips became common around 1995 because the electrically erasable PROM (EEPROM) chips are cheaper and easier to program than standard erasable PROM (EPROM) chips SONY VAIO VGN-FZ18 Battery .

EPROM chips may be erased by prolonged exposure to ultraviolet light, which accessed the chip via the window. Chip manufacturers use EPROM programmers (blasters) to program EPROM chips. Electrically erasable (EEPROM) chips come with the additional feature of allowing a BIOS reprogramming via higher-than-normal amounts of voltage SONY VAIO VGN-FZ21E Battery .

BIOS versions are upgraded to take advantage of newer versions of hardware and to correct bugs in previous revisions of BIOSes.

SONY VAIO VGN-FW31J Battery - 5200mAh/7800mAh/10400mAh, 11.10V

Beginning with the IBM AT, PCs supported a hardware clock settable through BIOS. It had a century bit which allowed for manually changing the century when the year 2000 happened

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. Most BIOS revisions created in 1995 and nearly all BIOS revisions in 1997 supported the year 2000 by setting the century bit automatically when the clock rolled past midnight, December 31, 1999.

The first flash chips were attached to the ISA bus SONY VAIO VGN-FW21E Battery .

Starting in 1997, the BIOS flash moved to the LPC bus, a functional replacement for ISA, following a new standard implementation known as "firmware hub" (FWH). In 2006, the first systems supporting a Serial Peripheral Interface (SPI) appeared, and the BIOS flash moved again SONY VAIO VGN-NR11S/S Battery .

The size of the BIOS, and the capacities of the ROM, EEPROM and other media it may be stored on, has increased over time as new features have been added to the code; BIOS versions now exist with sizes up to 16 megabytes SONY VAIO VGN-NR11M/S Battery .

Some modern motherboards are including even bigger NAND Flash ROM ICs on board which are capable of storing whole compact operating system distribution like some Linux distributions. For example, some recent ASUS motherboards included SplashTop Linux embedded into their NAND Flash ROM ICs SONY VAIO VGN-NR11Z/S Battery .

Flashing the BIOS

In modern PCs the BIOS is stored in rewritable memory, allowing the contents to be replaced or 'rewritten'. This rewriting of the contents is sometimes termed 'flashing'. This is done by a special program, usually provided by the system's manufacturer SONY VAIO VGN-NR11Z/T Battery .

A file containing such contents is sometimes termed 'a BIOS image'. A BIOS might be reflashed in order to upgrade to a newer version to fix bugs or provide improved performance or to support newer hardware, or a reflashing operation might be needed to fix a damaged BIOS. A Bios may also be "flashed" by putting the file on the root of a usb drive and booting Sony VAIO VGN-FZ21E Battery .

BIOS chip vulnerabilities

An American Megatrends BIOS registering the “Intel CPU uCode Error” while doing POST, most likely a problem with the POST.

EEPROM chips are advantageous because they can be easily updated by the user; hardware manufacturers frequently issue BIOS updates to upgrade their products, improve compatibility and remove bugs Sony VAIO VGN-FW21E Battery .

However, this advantage had the risk that an improperly executed or aborted BIOS update could render the computer or device unusable. To avoid these situations, more recent BIOSes use a "boot block"; a portion of the BIOS which runs first and must be updated separately Sony VAIO VGN-NR11S/S Battery .

This code verifies if the rest of the BIOS is intact (using hash checksums or other methods) before transferring control to it. If the boot block detects any corruption in the main BIOS, it will typically warn the user that a recovery process must be initiated by booting from removable media (floppy, CD or USB memory) so the user can try flashing the BIOS again Sony VAIO VGN-NR11Z/S Battery .

Some motherboards have a backup BIOS (sometimes referred to as DualBIOS boards) to recover from BIOS corruptions.

Overclocking

Some BIOS chips allow overclocking, an action in which the CPU is adjusted to a higher clock rate than its factory preset Sony VAIO VGN-NR11M/S Battery .

Overclocking may, however, seriously compromise system reliability in insufficiently cooled computers and generally shorten component lifespan. Overclocking, incorrectly performed, may also cause component temperatures to rise so quickly that they destroy themselves Sony VAIO VGN-NR11Z/T Battery .

Virus attacks

There are at least three known BIOS attack viruses, two of which were for demonstration purposes.

CIH

The first was a virus which was able to erase Flash ROM BIOS content, rendering computer systems unstable. CIH, also known as "Chernobyl Virus", appeared for the first time in mid-1998 and became active in April 1999 SONY VAIO VGN-FZ180E Battery .

It affected systems' BIOS's and often they could not be fixed on their own since they were no longer able to boot at all. To repair this, Flash ROM IC had to be removed from the motherboard to be reprogrammed elsewhere SONY VAIO VGN-FZ220E Battery .

Damage from CIH was possible since the virus was specifically targeted at the then widespread Intel i430TX motherboard chipset, and the most common operating systems of the time were based on the Windows 9x family allowing direct hardware access to all programs SONY VAIO VGN-FZ340E Battery .

Modern systems are not vulnerable to CIH because of a variety of chipsets being used which are incompatible with the Intel i430TX chipset, and also other Flash ROM IC types. There is also extra protection from accidental BIOS rewrites in the form of boot blocks which are protected from accidental overwrite or dual and quad BIOS equipped systems which may SONY VAIO VGN-FZ430E Battery ,

in the event of a crash, use a backup BIOS. Also, all modern operating systems like Linux, Mac OS X, Windows NT-based Windows OS like Windows 2000, Windows XP and newer, do not allow user mode programs to have direct hardware access. As a result, as of 2008, CIH has become essentially harmless SONY VAIO VGN-FZ460E Battery ,

at worst causing annoyance by infecting executable files and triggering alerts from antivirus software. Other BIOS viruses remain possible, however ; since Windows users without Windows Vista/7's UAC run all applications with administrative privileges, a modern CIH-like virus could in principle still gain access to hardware SONY VAIO VGN-FZ480E Battery .

Black Hat 2006

The second one was a technique presented by John Heasman, principal security consultant for UK based Next-Generation Security Software at the Black Hat Security Conference (2006), where he showed how to elevate privileges and read physical memory, using malicious procedures that replaced normal ACPI functions stored in flash memory SONY VAIO VGN-FZ4000 Battery .

Persistent BIOS Infection

The third one, known as "Persistent BIOS infection", was a method presented in CanSecWest Security Conference (Vancouver, 2009) and SyScan Security Conference (Singapore, 2009) where researchers Anibal Sacco and Alfredo Ortega, from Core Security Technologies SONY VAIO VGN-FZ31E Battery ,

demonstrated insertion of malicious code into the decompression routines in the BIOS, allowing for nearly full control of the PC at every start-up, even before the operating system is booted.

The proof-of-concept does not exploit a flaw in the BIOS implementation, but only involves the normal BIOS flashing proceduresSONY VAIO VGN-FZ31B Battery .

Thus, it requires physical access to the machine or for the user on the operating system to be root. Despite this, however, researchers underline the profound implications of their discovery: “We can patch a driver to drop a fully working rootkit. We even have a little code that can remove or disable antivirus SONY VAIO VGN-FZ31J Battery .”

Firmware on adapter cards

A computer system can contain several BIOS firmware chips. The motherboard BIOS typically contains code to access hardware components absolutely necessary for bootstrapping the system SONY VAIO VGN-FZ31M Battery ,

such as the keyboard (either PS/2 or on a USB human interface device), and storage (floppy drives, if available, and IDE or SATA hard disk controllers). In addition, plug-in adapter cards such as SCSI, RAID,Network interface cards, and video boards often include their own BIOS (e.g. Video BIOS) SONY VAIO VGN-FZ31Z Battery ,

complementing or replacing the system BIOS code for the given component. (This code is generally referred to as an option ROM.) Even devices built into the motherboard can behave in this way; their option ROMs can be stored as separate code on the main BIOS flash chip, and upgraded either in tandem with, or separately to, the main BIOS SONY VAIO VGN-FZ38M Battery .

An add-in card usually only requires an option ROM if it:

  • Needs to be used before the operating system can be loaded (usually this means it is required in the bootstrapping process), and
  • Is too sophisticated or specific a device to be handled by the main BIOS SONY VGP-BPS8 Battery

Older PC operating systems, such as MS-DOS (including all DOS-based versions of Microsoft Windows), and early-stage bootloaders, may continue to use the BIOS for input and output. However, the restrictions of the BIOS environment means that modern OSes will almost always use their own device drivers to directly control the hardware SONY VGP-BPS13/S Battery .

Generally, these device drivers only use BIOS and option ROM calls for very specific (non-performance-critical) tasks, such as preliminary device initialization.

In order to discover memory-mapped ISA option ROMs during the boot process SONY VGP-BPS13A/B Battery ,

PC BIOS implementations scan real memory from 0xC0000 to 0xF0000 on 2 KiB boundaries, looking for a ROMsignature: 0xAA55 (0x55 followed by 0xAA, since the x86 architecture is little-endian). In a valid expansion ROM, this signature is immediately followed by a single byte indicating the number of 512-byte blocks it occupies in real memory SONY VGP-BPS13B/B Battery .

The next byte contains an offset describing the option ROM's entry point, to which the BIOS immediately transfers control. At this point, the expansion ROM code takes over, using BIOS services to register interrupt vectors for use by post-boot applications, provide a user configuration interface, or display diagnostic information SONY VGP-BPS13A/S Battery .

There are many methods and utilities for examining the contents of various motherboard BIOS and expansion ROMs, such as Microsoft DEBUG or the UNIX dd.

BIOS boot specification

If the expansion ROM wishes to change the way the system boots (such as from a network device or a SCSI adapter for which the BIOS has no driver code) SONY VGP-BPS13AS Battery ,

it can use the BIOS Boot Specification(BBS) API to register its ability to do so. Once the expansion ROMs have registered using the BBS APIs, the user can select among the available boot options from within the BIOS's user interface Dell Inspiron 1320n Battery .

This is why most BBS compliant PC BIOS implementations will not allow the user to enter the BIOS's user interface until the expansion ROMs have finished executing and registering themselves with the BBS API Dell Inspiron 1464 Battery .

Changing role of the BIOS

Some operating systems, for example MS-DOS, rely on the BIOS to carry out most input/output tasks within the PC. A variety of technical reasons makes it inefficient for some recent operating systems written for 32-bit CPUs such as Linux and Microsoft Windows to invoke the BIOS directly Dell Inspiron 1564 Battery .

Larger, more powerful, servers and workstations using PowerPC or SPARC CPUs by several manufacturers developed a platform-independent Open Firmware (IEEE-1275), based on the Forth programming language. It is included with Sun's SPARC computers, IBM's RS/6000 line, and other PowerPC CHRP motherboards Dell Inspiron 1764 Battery .

Later x86-based personal computer operating systems, like Windows NT, use their own, native drivers which also makes it much easier to extend support to new hardware, while the BIOS still relies on a legacy 16-bit real mode runtime interface Dell Studio 1450 Battery .

There was a similar transition for the Apple Macintosh, where the system software originally relied heavily on the ToolBox—a set of drivers and other useful routines stored in ROM based on Motorola's 680x0 CPUs. These Apple ROMs were replaced by Open Firmware in the PowerPC Macintosh, then EFI in Intel Macintosh computers Dell Studio 1457 Battery .

Later BIOS took on more complex functions, by way of interfaces such as ACPI; these functions include power management, hot swapping, thermal management. To quote Linus Torvalds, the task of BIOS is "just load the OS and get the hell out of there" Dell Latitude D610 Battery .

However BIOS limitations (16-bit processor mode, only 1 MiB addressable space, PC AT hardware dependencies, etc.) were seen as clearly unacceptable for the newer computer platforms. Extensible Firmware Interface (EFI) is a specification which replaces the runtime interface of the legacy BIOS Toshiba NB100 Battery .

Initially written for the Itanium architecture, EFI is now available for x86 and x86-64 platforms; the specification development is driven by The Unified EFI Forum, an industry Special Interest Group.

Linux has supported EFI via the elilo and GRUB boot loaders Toshiba Satellite M65 battery .

The Open Source community increased their effort to develop a replacement for proprietary BIOSes and their future incarnations with an open sourced counterpart through the coreboot and OpenBIOS/Open Firmware projects. AMD provided product specifications for some chipsets, and Google is sponsoring the project Toshiba Satellite M60 battery .

Motherboardmanufacturer Tyan offers coreboot next to the standard BIOS with their Opteron line of motherboards. MSI and Gigabyte Technology have followed suit with the MSI K9ND MS-9282 and MSI K9SD MS-9185 resp. the M57SLI-S4 models Dell Latitude D830 Battery .

Some BIOSes contain a "SLIC", a digital signature placed inside the BIOS by the manufacturer, for example Dell. This SLIC is inserted in the ACPI table and contains no active code. Computer manufacturers that distribute OEM versions of Microsoft Windows and Microsoft application software can use the SLIC to authenticate licensing to the OEM Windows Installation disk and/or systemrecovery disc containing Windows software Dell Latitude D620 Battery .

Systems having a SLIC can be activated with an OEM Product Key, and they verify an XML formatted OEM certificate against the SLIC in the BIOS as a means of self-activating. If a user performs a fresh install of Windows, they will need to have possession of both the OEM key and the digital certificate for their SLIC in order to bypass activation Dell Inspiron Mini 10 Battery ;

in practice this is extremely unlikely and hence the only real way this can be achieved is if the user performs a restore using a pre-customised image provided by the OEM.

Recent Intel processors (P6 and P7) have reprogrammable microcode Sony VGN-FW11S Battery .

The BIOS may contain patches to the processor code to allow errors in the initial processor code to be fixed, updating the processor microcode each time the system is powered up. Otherwise, an expensive processor swap would be required Sony VGN-FW11M Battery .

For example, the Pentium FDIV bug became an expensive fiasco for Intel that required a product recall because the original Pentium did not have patchable microcode.

The BIOS business

The vast majority of PC motherboard suppliers license a BIOS "core" and toolkit from a commercial third-party, known as an "independent BIOS vendor" or IBV Sony VGN-FW139E/H battery .

The motherboard manufacturer then customizes this BIOS to suit its own hardware. For this reason, updated BIOSes are normally obtained directly from the motherboard manufacturer.

Major BIOS vendors include American Megatrends (AMI), Insyde Software, Phoenix Technologies and Byosoft Dell Latitude E5400 Battery .

Former vendors include Award Software and Microid Research which were acquired byPhoenix Technologies in 1998. Phoenix has now phased out the Award Brand name. General Software, which was also acquired by Phoenix in 2007, sold BIOS for Intel processor based embedded systems Dell Latitude E4200 Battery .

In computing, booting (also known as "booting up") is a bootstrapping process that starts operating systems when the user turns on a computer system. A boot sequence is the initial set of operations that the computer performs when power is switched on. The boot loader typically loads the main operating system for the computer Dell Inspiron 300M Battery .

History

The computer word boot is short for "bootstrap" (itself short for "bootstrap load"). The term bootstrap derives from the idiom: to pull oneself up by one's bootstraps Dell Vostro A840 Battery .

The term refers to the fact that a computer cannot run without first loading software but must be running before any software can be loaded, which seems as impossible as to "pull yourself up by your own bootstraps Dell Studio 1737 battery ."

In computers in the 1950s, pressing a bootstrap button caused a hardwired program to read a bootstrap program from a punched card in a card reader, a magnetic tape in a tape drive, or a magnetic drum unit or magnetic disk drive, and then execute the loaded boot program Dell Inspiron E1505 battery ,

which loaded a larger system of programs from that medium into memory without further help from the human operator. The term "boot" has been used in this sense since at least 1958. For example, in the IBM 701 computer (1952–1956) which had a "load" button that initiated reading of the first 36-bit word from a punched card, a magnetic tape, or a magnetic drum unit Dell RM791 battery .

The left 18-bit half-word was then executed as an instruction, which read additional words into memory. Similarly, the IBM 1401 system (c. 1958) used a card reader to load application program from punched cards Dell XPS M1530 battery .

The 80 characters stored in each punched card were read into memory locations 001 to 080, then the computer would branch to memory location 001 to read its first stored instruction, as read in from the punched card Dell XPS M2010 battery .

This instruction was always the same: move the information in these first 80 memory locations to an assembly area where the information in punched cards 2, 3, 4, and so on, could be combined to form the stored program Acer Aspire One battery .

Once this information was moved to the assembly area, the machine would branch to an instruction in location 080 (read a card) and the next card would be read and its information processed. Esentially, the process was one where each subsequent card was "bootstrapped" into memory by the prtevious punched card Toshiba Satellite P10 Battery .

The CDC 6600 (c. 1964) had a dead start panel with 144 toggle switches; the dead start switch entered 12 words from the toggle switches to the memory of peripheral processor (PP) 0 and initiated the load sequence. PP 0 loaded the necessary code into its own memory and then initialized the other PP's SONY VGN-FZ210CE Battery .

The GE 645 (c. 1965) had a "BOOT" button. It is possible that the contraction from "bootstrap" to "boot" was motivated by an inclination to label the button with fewer, larger characters, or the contraction may follow the familiar habit of contracting words to make them easier to say, and to create insider jargon Dell Precision M70 Battery .

Some machines, like the Atari ST microcomputer, were "instant-on" with the operating system executing from a ROM. Retrieval of the OS from secondary or tertiary store was thus eliminated as one of the characteristic operations for bootstrapping Toshiba Satellite L305 Battery .

To accommodate system customization for loading accessories and other support software automatically, as part of the boot process, the Atari's floppy drive was read for the additional components. There was a timeout delay, allowing time to manually insert a floppy, as the system searched for the extra components, which could be avoided by inserting a blank disk Toshiba Satellite T4900 Battery .

The Multics operating system (c. 1967) had a boot command. Multics documents also refer to "boot tapes," but it is hard to determine exactly when that term was first used.

In the Unix operating system, the earliest reference for "boot" is probably in The Unix Programmer's Manual, first edition 1971.11.03 Toshiba PA3399U-2BRS battery .

Boot loader

A computer's central processor can only execute program code found in read-only memory (ROM), random access memory (RAM) or an operator's console Toshiba Satellite A200 Battery .

Modern operating systems and application program code and data are stored on nonvolatile data storage devices, such as hard disk drives, CD, DVD, flash memory cards (like an SD card), USB flash drive, and floppy disk. When a computer is first powered on, it usually does not have an operating system in ROM or RAM Toshiba Satellite 1200 Battery .

The computer must execute a relatively small program stored in ROM along with the bare minimum of data needed to access the nonvolatile devices from which the operating system programs and data are loaded into RAM Toshiba Satellite M300 Battery .

The small program that starts this sequence of loading into RAM is known as a bootstrap loader, bootstrap or boot loader. This small boot loader program's only job is to load other data and programs which are then executed from RAM SONY VGP-BPS13A/Q Battery.

Often, multiple-stage boot loaders are used, during which several programs of increasing complexity sequentially load one after the other in a process of chain loading SONY VGP-BPS13A/Q Battery .

Early computers (such as the IBM 650, DEC PDP-1 through PDP-8 and early models of the PDP-11) had a row of dials or toggle switches on the front panel to allow the operator to manually enter the boot instructions into memory before transferring control to the CPU, or to directly pass an instruction to the CPU SONY VGP-BPS13B/Q Battery .

The boot loader would then read in either the second-stage boot loader (called Binary Loader of paper tape with checksum), or the operating system from an outside storage medium such as paper tape, punched card, or a disk drive SONY VGP-BPS13B/Q Battery .

Pseudo-assembly code for the bootloader might be as simple as the following eight instructions:

  1. Set the P register to 9
  2. Check paper tape reader ready
  3. If not ready, jump to 2 SONY VGP-BPS13/Q Battery
  4. Read a byte from paper tape reader to accumulator
  5. If end of tape, jump to 9
  6. Store accumulator to address in P register
  7. Increment the P register SONY VGP-BPS13/Q Battery
  8. Jump to 2

A related example is based on a loader for a 1970's Nicolet Instrument Corporation minicomputer. Note that the bytes of the second-stage loader are read from paper tape in reverse order SONY VGP-BPS21A/B Battery .

  1. Set the P register to 106
  2. Check paper tape reader ready
  3. If not ready, jump to 2 SONY VGP-BPS21/S Battery
  4. Read a byte from paper tape reader to accumulator
  5. Store accumulator to address in P register
  6. Decrement the P register
  7. Jump to 2 SONY VGP-BPS21B Battery

The length of the second stage loader is such that the final byte overwrites location 7. After the instruction in location 6 executes, location 7 starts the second stage loader executing. The second stage loader then waits for the much longer tape containing the operating system to be placed in the tape reader SONY VGP-BPS21A Battery .

The difference between the boot loader and second stage loader is the addition of checking code to trap paper tape read errors, a frequent occurrence with the hardware of the time, which in this case was an ASR-33 teletype SONY VGP-BPS21 Battery .

Some computer systems, upon receiving a boot signal from a human operator or a peripheral device, may load a very small number of fixed instructions into memory at a specific location, initialize at least one CPU, and then point the CPU to the instructions and start their execution Sony VGP-BPS21A/B Battery .

These instructions typically start an input operation from some peripheral device (which may be switch-selectable by the operator). Other systems may send hardware commands directly to peripheral devices or I/O controllers that cause an extremely simple input operation Sony VGP-BPS21/S Battery

(such as "read sector zero of the system device into memory starting at location 1000") to be carried out, effectively loading a small number of bootload instructions into memory; a completion signal from the I/O device may then be used to start execution of the instructions by the CPU Sony VGP-BPS21A Battery .

Smaller computers often use less flexible but more automatic bootload mechanisms to ensure that the computer starts quickly and with a predetermined software configuration. In many desktop computers, for example, the bootstrapping process begins with the CPU executing software contained in ROM Sony VGP-BPS21 Battery

(for example, the BIOS of an IBM PC) at a predefined address (some CPUs, including the Intel x86 series are designed to execute this software after reset without outside help). This software contains rudimentary functionality to search for devices eligible to participate in booting, and load a small program from a special section (most commonly the boot sector) of the most promising device Sony Vaio PCG-5G2L Battery .

Boot loaders may face peculiar constraints, especially in size; for instance, on the IBM PC and compatibles, the first stage of boot loaders located on hard drives must fit into the first 446 bytes (or 440 bytes if Windows NT or above has to be supported because NT put 6 byte disk-signature starting from offset 440) Sony Vaio PCG-5G3L Battery

of the Master Boot Record, in order to leave room for the 64-byte partition table and the 2-byte 0xAA55 'signature', which the BIOS requires for a proper boot loader.

Some operating systems, most notably pre-1995 Macintosh systems from Apple Sony Vaio PCG-5J1L Battery ,

are so closely interwoven with their hardware that it is impossible to natively boot an operating system other than the standard one. This is the opposite extreme of the bootload using switches mentioned above; it is highly inflexible but relatively error-proof and foolproof as long as all hardware is working normally Sony Vaio PCG-5K2L Battery .

A common solution in such situations is to design a bootloader that works as a program belonging to the standard OS that hijacks the system and loads the alternative OS. This technique was used by Apple for its A/UX Unix implementation and copied by various freeware operating systems and BeOS Personal Edition 5 Sony Vaio PCG-5J2L Battery .

The Atari ST also had its operating system in ROM but, by inserting the Spectre GCR cartridge with the Macintosh system ROM in the game slot and turning the Atari on, it could "natively boot" the Macintosh operating system rather than Atari's own TOS system Sony Vaio PCG-5K1L Battery .

The Atari ST hardware was designed so the cartridge slot could provide native program execution for gaming purposes as a holdover from Atari's legacy making electronic games.

Second-stage boot loader

The small program is most often not itself an operating system, but only a second-stage boot loader, such as GRUB, BOOTMGR, Syslinux, LILO or NTLDR Sony Vaio PCG-6S2L Battery .

It will then be able to load the operating system properly, and finally transfer execution to it. The operating system will initialize itself, and may load device drivers that are needed for the normal operation of the OS. After that it starts loading normal system programs Sony Vaio PCG-6S3L Battery .

Many bootloaders (like GRUB, BOOTMGR, LILO, and NTLDR) can be configured to give the user multiple booting choices. These choices can include different operating systems (for dual or multi-booting from different partitions or drives), different versions of the same operating system (in case a new version has unexpected problems) Sony Vaio PCG-6V1L Battery ,

different operating system loading options (e.g., booting into a rescue or safe mode) or some standalone program that can function without an operating system, such as memory testers (e.g., memtest86+) or even games (see List of PC Booter games) Sony Vaio PCG-6W1L Battery .

Usually a default choice is preselected with a time delay during which you can press a key to change the choice, after which the default choice is automatically run, so normal booting can occur without interaction.

The boot process can be considered complete when the computer is ready to interact with the user, or the operating system is capable of running system programs or application programs Sony Vaio PCG-6W2L Battery .

Typical modern personal computers boot in about one minute (of which about 15 seconds are taken by a power-on self test (POST) and a preliminary boot loader, and the rest by loading the operating system and other software Sony Vaio PCG-6W3L Battery .

Time spent after the operating system loading can be considerably shortened by bringing the system with all cores at once, as with coreboot in as little as 3 seconds, whereas large servers may take several minutes to boot and start all their services Sony Vaio PCG-7111L Battery .

Many embedded systems must boot immediately. For example, waiting a minute for a digital television or sat-nav to start is generally unacceptable. Therefore such devices have software system in ROM or flash memory so the device can begin functioning immediately Sony Vaio PCG-7112L Battery .

For these types of embedded system little or no loading is necessary, since the loading can be precomputed and stored on the ROM when the device is made.

Large and complex systems may have boot procedures that proceed in multiple phases, each phase loading a more complex version of itself, until finally the operating system and other software are loaded and ready to execute Sony Vaio PCG-7113L Battery .

Because operating systems are designed as if they never start or stop, bootload processes sometimes load the operating system, configure themselves as a mere process within that system, and then irrevocably transfer control to the operating system Sony Vaio PCG-7133L Battery .

The bootload process then terminates normally as any other process would, and the user need not have any awareness of the bootload.

Network booting

Most computers are also capable of booting over a computer network Sony Vaio PCG-7Z2L Battery .

In this scenario, the operating system is stored on the disk of a server, and certain parts of it are transferred to the client using a simple protocol such as the Trivial File Transfer Protocol. After these parts have been transferred, the operating system then takes over control of the booting process Sony Vaio PCG-8Y1L Battery .

Boot devices (IBM PC)

The boot device is the device from which the operating system is loaded. A modern PC BIOS supports booting from various devices, typically a local hard disk drive (or one of several partitions on such a disk) Sony Vaio PCG-8Y2L Battery ,

an optical disc drive, a USB device (flash drive, hard disk drive, optical disc drive, etc.), a flash memory card such as an SD card in a multi-media card slot, or a network interface card (usingPXE). Older, less common bootable devices include floppy disk drives, SCSI devices, Zip drives, and LS-120 drives Sony Vaio PCG-8Z1L Battery .

Typically, the BIOS will allow the user to configure a boot order. If the boot order is set to "firstly, the DVD drive; secondly, the hard disk drive", then the BIOS will try to boot from the DVD drive, and if this fails (e.g. because there is no DVD in the drive), it will try to boot from the local hard drive Sony Vaio PCG-8Z2L Battery .

For example, on a PC with Windows XP installed on the hard drive, the user could set the boot order to that given above, and then insert a GNU/Linux Live CD in order to try out Linux without having to install an operating system onto the hard drive Sony VAIO PCG-5G2L Battery .

This is an example of dual booting - the user choosing which operating system to start after the computer has performed its Power On Self Test. In this example of dual booting, the user chooses by inserting or removing the CD from the computer, but it is more common to choose which operating system to boot by selecting from a menu using the computer keyboard Sony VAIO PCG-5G3L Battery .

Boot sequence on standard PC (IBM-PC compatible)

Upon starting, a personal computer's x86 CPU runs the instruction located at the memory location CS:IP F000:FFF0 of the BIOS, which is located at the 0xFFFF0 linear address Sony VAIO PCG-5J1L Battery .

This memory location is close to the end of the 1MB of system memory accessible in real mode. It typically contains a jump instruction that transfers execution to the location of the BIOS start-up program. This program runs a power-on self test (POST) to check and initialize required devices Sony VAIO PCG-5K2L Battery .

The BIOS goes through a pre-configured list of non-volatile storage devices ("boot device sequence") until it finds one that is bootable. A bootable device is defined as one that can be read from, and the last two bytes of the first sector contain the word 0xAA55 (also known as the boot signature) Sony VAIO PCG-5J2L Battery .

Once the BIOS has found a bootable device it loads the boot sector to hexadecimal Segment:Offset address 0000:7C00 or 07C0:0000 (maps to the same ultimate address) and transfers execution to the boot code. In the case of a hard disk, this is referred to as the master boot record (MBR) and is often not operating system specific Sony VAIO PCG-5K1L Battery .

The conventional MBR code checks the MBR's partition table for a partition set as bootable (the one with active flag set). If an active partition is found, the MBR code loads the boot sector code from that partition and executes it. The boot sector is often operating-system-specific Sony VAIO PCG-5L1L Battery ;

however, in most operating systems its main function is to load and execute the operating system kernel, which continues startup. If there is no active partition, or the active partition's boot sector is invalid, the MBR may load a secondary boot loader which will select a partition (often via user input) and load its boot sector, which usually loads the corresponding operating system kernel Sony VAIO PCG-6S2L Battery .

Some systems (particularly newer Macintoshes) use Intel's proprietary EFI. Also coreboot allows a computer to boot without having an over-complicated firmware/BIOS constantly running in system management mode. The legacy 16-bit BIOS interfaces are required by certain x86 operating systems, such as Windows Sony VAIO PCG-6S3L Battery .

However most boot loaders have 16-bit support for these legacy BIOS systems.

Most PCs, if a BIOS chip is present, will show a screen detailing the BIOS chip manufacturer, copyright held by the chip's manufacturer and the ID of the chip at startup Sony VAIO PCG-6V1L Battery .

At the same time, it also shows the amount of computer memory available and other pieces of information about the computer.

Power On Self Test (POST)

The computer power-on self-test tests the computer to make sure it meets the necessary system requirements and that all hardware is working properly before starting the remainder of the boot process Sony VAIO PCG-6W1L Battery .

If the computer passes the POST, the computer may have a single beep (with some computer BIOS suppliers it may beep twice) as the computer starts and the computer will continue to start normally.

Other kinds of boot sequences Sony VAIO PCG-6W2L Battery

Some other processors have other kinds of boot modes:

1) There are alternative techniques for booting CPUs and microcontrollers Sony VAIO PCG-6W3L Battery :

  • Some modern CPUs and microcontrollers (for example, TI OMAP) or sometimes even DSPs may have boot ROM with boot code integrated directly into their silicon, so such a processor could perform quite a sophisticated boot sequence on its own and load boot programs from various sources like NAND flash, SD or MMC card and so on Sony VAIO PCG-7111L Battery .
  • It is hard to hardwire all the required logic for handling such devices, so an integrated boot ROM is used instead in such scenarios. Boot ROM usage enables more flexible boot sequences than hardwired logic could provide. For example, the boot ROM could try to perform boot from multiple boot sources Sony VAIO PCG-7112L Battery .
  • Also, a boot ROM is often able to load a boot loader or diagnostic program via serial interfaces like UART, SPI, USB and so on. This feature is often used for system recovery purposes when for some reasons usual boot software in non-volatile memory got erased Sony VAIO PCG-7113L Battery .
  • This technique could also be used for initial non-volatile memory programming when there is clean non-volatile memory installed and hence no software available in the system yet.
  • It is also possible to take control of a system by using a hardware debug interface such as JTAG Sony VAIO PCG-7Z1L Battery .
  • Such an interface may be used to write the boot loader program into bootable non-volatile memory (e.g. flash) by instructing the processor core to perform the necessary actions to program non-volatile memory. Alternatively, the debug interface may be used to upload some diagnostic or boot code into RAM, and then to start the processor core and instruct it to execute the uploaded code Sony VAIO PCG-7Z2L Battery .
  • This allows, for example, the recovery of embedded systems where no software remains on any supported boot device, and where the processor does not have any integrated boot ROM. JTAG is a standard and popular interface; many CPUs, microcontrollers and other devices are manufactured with JTAG interfaces (as of 2009) Sony VAIO PCG-8Y1L Battery .
  • Some microcontrollers provide special hardware interfaces which can't be used to take arbitrary control of a system or directly run code, but instead they allow the insertion of boot code into bootable non-volatile memory (like flash memory) via simple protocols WD passport essential (500GB/640GB) .
  • Then at the manufacturing phase, such interfaces are used to inject boot code (and possibly other code) into non-volatile memory. After system reset, the microcontroller begins to execute code programmed into its non-volatile memory, just like usual processors are using ROMs for booting WD passport essential (250GB/320GB) .
  • Most notably this technique is used by Atmel AVR microcontrollers, and by others as well. In many cases such interfaces are implemented by hardwired logic. In other cases such interfaces could be created by software running in integrated on-chip boot ROM from GPIO pins WD passport essential SE (750GB/1TB .

2) Most digital signal processors have the following boot modes:

It is worthwhile mentioning that in case of DSPs there is often a second microprocessor or microcontroller present in the system design, and this is responsible for overall system behavior, interrupt handling, dealing with external events, user interface, etc. while the DSP is dedicated to signal processing tasks only WD passport elite(500GB/640GB) .

In such systems the DSP could be booted by another processor which is sometimes referred as the host processor (giving name to a Host Port). Such a processor is also sometimes referred as the master, since it usually boots first from its own memories and then controls overall system behavior, including booting of the DSP, and then further controlling the DSP's behavior WD passport studio for Mac(320GB/500GB) .

An interesting thing here is that the DSP often lacks its own boot memories and relies on the host processor to supply the required code instead. The most notable systems with such a design are cell phones, modems, audio and video players, etc. where a DSP and a CPU/microcontroller are co-existing WD passport studio for Mac(500GB/640GB) .

Many FPGA chips load their configuration from an external serial EEPROM ("configuration ROM") on power-up.

Initial Program Load

In current IBM mainframe systems, the boot process is known as Initial Program Load (IPL) WD Elements series(250GB/320GB).

The term was coined by IBM for the design of the System/360 and continues to be used in those environments today. In systems that share the System/360 heritage—and in some that have been inspired by it, including smaller systems such as the IBM 1130—IPL is a hardware function, not a program run on the system itself WD Elements SE(500GB/640GB) .

In the smaller S/360 processors, an IPL is initiated by the computer operator by selecting the (three hexadecimal digit) device address using rotary switches on the computer console, followed by pressing the LOAD button WD Elements SE(750GB/1TB) .

The IPL function in the System/360 and its successors reads 24 bytes from an operator-specified or pre-configured device into memory starting at location zero. The second and third groups of eight bytes are treated as Channel Command Words (CCWs) to continue loading the startup program WD Elements desktop(500GB/640GB) .

When the I/O channel commands are complete, the first group of eight bytes is then loaded into the Program Status Word (PSW) register and the startup program begins execution at the designated location. The boot device is usually a disk drive, but exactly the same procedure is also used to boot from other devices WD Elements desktop(750GB/1TB) ,

such as tape drives, or even card readers, in a device-independent manner, allowing e.g. the installation of an operating system on a pristine computer from a magnetic distribution tape. Of course, the disk, tape or card deck must contain a special program to load the actual operating system into memory WD Elements desktop(1.5 TB/2TB) ,

a multi-stage procedure similar to most booting procedures (see elsewhere in this article).

A noteworthy variation of this is found on the Burroughs B1700 where there is neither a bootstrap ROM nor a hardwired IPL operation WD passport essential SE (750GB/1TB)--USB 3.0 .

Instead, after the system is reset it reads and executes opcodes sequentially from a tape drive mounted on the front panel; this sets up a boot loader in RAM which is then executed WD passport essential (500GB/640GB) .

However, since this makes few assumptions about the system it can equally well be used to load diagnostic (Maintenance Test Routine) tapes which display an intelligible code on the front panel even in cases of gross CPU failure.

Rebooting

There is some ambiguity in the nomenclature for rebooting, as discussed below WD passport for Mac(320GB/500GB) .

Hard reboot

A hard reboot (also known as a cold reboot, cold boot or cold start) is when power to a computer is abruptly turned off, then turned back on. This starts the computer without first performing any shut-down procedure (With many operating systems, especially those using disk caches WD passport for Mac(640GB/1TB) ,

after a hard reboot the filesystem may be in an "unclean" state, and an automatic scan of on-disk filesystem structures will be done before normal operation can begin.) It may be caused by power failure, be done by accident, or be done deliberately as a last resort to forcibly retrieve the system from instances of a system freeze My book essential 4 generation (640GB/1TB) ,

critical error or virus-inflicted DoS attack. It can also be used by intruders to access cryptographic keys from RAM, in which case it is called a cold boot attack. The attack relies on the data remanence property of DRAM and SRAM to retrieve memory contents which remain readable in the seconds to minutes after power has been removed WD My book essential 4 generation( 1.5TB/2TB) .

However, other types of reset also disrupt the operating system in the same manner as power loss:

Soft reboot

A soft reboot (also known as a warm reboot) is restarting a computer under software control, without removing power or (directly) triggering a reset line. It usually, though not always, refers to an orderlyshutdown and restarting of the machine WD My book studio(1TB/2TB) .

The Control-Alt-Delete key combination on the original PC from Sphere 1 was designed to allow a soft reboot reducing wear on the hardware. This kind of reboot will not usually reset the hard disks, so that they have time to update their write cache to permanent storage WD My book essential 4 generation( 1.5TB/2TB) .

Hard disks will also keep their configuration (like C/H/S adjustments, HPA, DCO, internal passwords...) over these reboots.

The Linux kernel has optional support for the kexec system call, which transfers execution to a new kernel and skips hardware or firmware reboot WD My book elite(640GB/2TB) .

Saturday, February 19, 2011

Internet Explorer

Windows Internet Explorer (formerly Microsoft Internet Explorer; commonly abbreviated to IE or MSIE), is a series of graphical web browsersdeveloped by Microsoft and included as part of the Microsoft Windows line of operating systems starting in 1995 (Dell XPS M1210 Battery) http://www.hdd-shop.co.uk .

It was first released as part of the add-on package Plus! for Windows 95 that year. Later versions were available as free downloads, or in service packs, and included in the OEM service releases of Windows 95 and later versions of Windows Dell Studio XPS 1640 Battery .

IE has been the most widely used web browser since 1999, attaining a peak of about 95% usage share during 2002 and 2003 with IE5 andIE6. Since its peak of popularity, its usage share has declined in the face of renewed competition from other web browsers to 55%, and is slowly trending downward Dell Vostro 1710 Battery .

Microsoft spent over $100 million per year on IE in the late 1990s, with over 1000 people working on it by 1999.

Since its first release, Microsoft has added features and technologies such as basic table display (in version 1.5); XMLHttpRequest (in version 5), which aids creation of dynamic web pages Dell KM958 battery ;

and Internationalized Domain Names (in version 7), which allow Web sites to have native-language addresses with non-Latin characters. The browser has also received scrutiny throughout its development for use of third-party technology (such as the source code of Spyglass Mosaic, used without royalty in early versions) Dell Studio 1555 battery

and security and privacy vulnerabilities, and both the United States and the European Unionhave alleged that integration of IE with Windows has been to the detriment of other browsers.

The latest stable release is Internet Explorer 8, which is available as a free update for Windows XP with Service Pack 2 or later Sony VGP-BPS13 battery ,

Windows Server 2003with Service Pack 1 or later, Windows Vista, and Windows Server 2008, and is included with Windows 7 and Windows Server 2008 R2. Internet Explorer was originally planned to be omitted from Windows 7 and Windows Server 2008 R2 in Europe but Microsoft later dropped the plans Sony VGP-BPS13/B battery ,

and instead included a browser ballot screen with the products, allowing users to select a different web browser if they wish.

Versions of Internet Explorer for other operating systems have also been produced, including an embedded OEM version called Internet Explorer Mobilewhich is currently based on IE7 Sony VGP-BPS13/S battery .

Pocket Internet Explorer, later rebranded Internet Explorer Mobile, which is made for Windows Phone 7, Windows CE, and previously Windows Mobile, remains in development alongside the more advanced desktop versions. Internet Explorer for Mac and Internet Explorer for UNIX (Solaris and HP-UX) have been discontinued Sony VGP-BPS13A/B battery .

he Internet Explorer project was started in the summer of 1994[citation needed] by Thomas Reardon, using source code from Spyglass, Inc.Mosaic, an early commercial web browser with formal ties to the pioneering NCSA Mosaic browser. In late 1994, Microsoft licensed Spyglass Mosaic for a quarterly fee plus a percentage of Microsoft's non-Windows revenues for the software Sony VGP-BPS13B/B battery .

Although bearing a name similar to NCSAMosaic, Spyglass Mosaic had used the NCSA Mosaic source code sparingly.

Internet Explorer 1 made its debut on August 16, 1995. It was a reworked version of Spyglass Mosaic, which Microsoft had licensed, like many other companies initiating browser development, from Spyglass Inc Sony VGP-BPL9 battery .

It came with Microsoft Plus! for Windows 95 and the OEM release of Windows 95. It was installed as part of the Internet Jumpstart Kitin Plus!.[11] The Internet Explorer team began with about six people in early development. Internet Explorer 1.5 was released several months later for Windows NT and added support for basic table rendering Sony VGP-BPS13B/B battery .

However, by including it for free on their OS, they did not have to pay royalties to Spyglass Inc., which resulted in a lawsuit and a multi-million USD settlement.

Internet Explorer 2 was released for Windows 95, Windows NT 3.5, and NT 4.0 on November 22, 1995 (following a 2.0 beta in October). It featured support for SSL, cookies, VRML, RSA, and Internet newsgroups Sony VGP-BPL15 battery .

Version 2 was also the first release for Windows 3.1 and Macintosh System 7.0.1 (PPC or 68k), although the Mac version was not released until January 1996 for PPC, and April for 68k.Version 2.1 for the Mac came out in August 1996, although by this time, Windows was getting 3.0 Dell Inspiron E1505 battery .

Version 2 was included in Windows 95 OSR 1 and Microsoft's Internet Starter Kit for Windows 95 in early 1996. It launched with twelve languages including English but this expanded to 24, 20, and 9 for Win 95, Win 3.1, and Mac respectively by April 1996. The 2.0i version supported double-byte character-set Dell Latitude E6400 battery .

Internet Explorer 3 was released on August 13, 1996, and went on to be much more popular than its predecessors. Internet Explorer 3 was the first major browser with CSS support, although this support was only partial. It also introduced support for ActiveX controls, Java applets, inline multimedia, and the PICS system for content metadata HP Pavilion dv6000 Battery .

Version 3 also came bundled with Internet Mail and News, NetMeeting, and an early version of the Windows Address Book, and was itself included with Windows 95 OSR 2. Version 3 proved to be the first more popular version of Internet Explorer, which brought with it increased scrutiny SONY VAIO VGN-FZ Battery .

In the months following its release, a number of security and privacy vulnerabilities were found by researchers and hackers. This version of Internet Explorer was the first to have the 'blue e' logo. The Internet Explorer team consisted of roughly 100 people during the development of three months SONY VAIO VGN-FZ18 Battery .

The first major IE security hole, the Princeton Word Macro Virus Loophole, was discovered on August 22, 1996 in IE3. Backwards compatibility was handled by allowing users who upgraded to IE3 to still use the last IE, because the installation converted the previous version to a separate directory SONY VAIO VGN-FZ21E Battery .

Internet Explorer 4, released in September 1997, deepened the level of integration between the web browser and the underlying operating system. Installing version 4 on a Windows 95 or Windows NT 4 machine and choosing Windows Desktop Update would result in the traditional Windows Explorer being replaced by a version more akin to a web browser interface, as well as the Windows desktop itself being web-enabled via Active Desktop SONY VAIO VGN-FW21E Battery .

The integration with Windows, however, was subject to numerous packaging criticisms (see United States v. Microsoft). This option was no longer available with the installers for later versions of Internet Explorer but was not removed from the system if already installed SONY VAIO VGN-NR11S/S Battery .

Internet Explorer 4 introduced support for Group Policy, allowing companies to configure and lock down many aspects of the browser's configuration as well as support for offline browsing.Internet Mail and News was replaced with Outlook Express, and Microsoft Chat and an improved NetMeeting were also included SONY VAIO VGN-NR11M/S Battery .

This version also was included with Windows 98. New features were added that allow you to save and retrieve posts in comment forms which are still not being used today. Internet Explorer 4.5 offered new features such as easier 128-bit encryption. It also offered a dramatic stability improvement over prior versions, particularly the 68k version which was especially prone to freezingSONY VAIO VGN-NR11Z/S Battery .

Internet Explorer 5, launched on March 18, 1999, and subsequently included with Windows 98 Second Edition and bundled with Office 2000, was another significant release that supported bi-directional text, ruby characters, XML, XSLT, and the ability to save web pages in MHTML format SONY VAIO VGN-NR11Z/T Battery .

IE5 was bundled with Outlook Express 5. Also, with the release of Internet Explorer 5.0, Microsoft released the first version of XMLHttpRequest, giving birth to Ajax (even though the term "Ajax" wasn't coined until years later). It was the last with a 16-bit version Sony VAIO VGN-FZ21E Battery .

Internet Explorer 5.01, a bug fix version, was released in December 1999. Windows 2000 includes this version. Internet Explorer 5.5 followed in July 2000, improving its print preview capabilities, CSS and HTML standards support, and developer APIs; this version was bundled withWindows Me Sony VAIO VGN-FW21E Battery .

However, version 5 was the last version for Mac and UNIX. Version 5.5 was the last to have Compatibility Mode, which allowed Internet Explorer 4 to be run side by side with the 5.x. The IE team consisted of over 1,000 people by 1999, with funding on the order of 100 million USD per year Sony VAIO VGN-NR11S/S Battery .

Internet Explorer 7 was released on October 18, 2006. It includes bug fixes, enhancements to its support for web standards, tabbed browsing with tab preview and management, a multiple-engine search box, a web feeds reader, Internationalized Domain Name support (IDN), Extended Validation Certificate support, and anti-phishing filter Sony VAIO VGN-NR11Z/S Battery .

With IE7, Internet Explorer has been decoupled from the Windows Shell—unlike previous versions, the Internet Explorer ActiveX control is not hosted in the Windows Explorer process, but rather runs in a separate Internet Explorer process Sony VAIO VGN-NR11M/S Battery .

It is included with Windows Vista and Windows Server 2008, and is available for Windows XP Service Pack 2 and later, and Windows Server 2003 Service Pack 1 and later. The original release of Internet Explorer 7 required the computer to pass a Windows Genuine Advantage validation check prior to installing, but on October 5, 2007, Microsoft removed this requirement Sony VAIO VGN-NR11Z/T Battery .

As some statistics show, by mid-2008, Internet Explorer 7 market share exceeded that of Internet Explorer 6 in a number of regions.

Internet Explorer 8 was released on March 19, 2009. It had been in development since August 2007 at the latest. On March 5, 2008, the first public beta (Beta 1) was released to the general public SONY VAIO VGN-FZ180E Battery .

On August 27, 2008, the second public beta (Beta 2) was released. It is supported in Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista, Windows 7, and Windows Server 2008 on both 32-bit as well as 64-bit architectures. Internet Explorer 8 (IE8) RC1 was released on January 26, 2009 SONY VAIO VGN-FZ220E Battery .

Internet Explorer 8 "Final" was released on March 19, 2009. Security, ease of use, and improvements in RSS,CSS, and Ajax support are Microsoft's priorities for IE8. It includes much stricter compliance with web standards, including a planned full Cascading Style Sheets 2.1 compliance for the release version SONY VAIO VGN-FZ340E Battery .

All these changes allow Internet Explorer 8 to pass the Acid2 test. However, to prevent compatibility issues, IE8 also includes the IE7 rendering behavior. Sites that expect IE7 quirks can disable IE8's breaking changes by including a meta element in the HEAD section of the HTML document SONY VAIO VGN-FZ430E Battery .

IE8 also includes numerous improvements to JavaScript support as well as performance improvements, although it still does not pass the Acid3 test, with version 8.0 scoring 20/100. It includes support for Accelerators—which allow supported web applications to be invoked without explicitly navigating to them—and WebSlices—which allows portions of page to be subscribed to and monitored from a redesigned Favorites Bar SONY VAIO VGN-FZ460E Battery .

Other features include InPrivate privacy features and SmartScreen phishing filter.

Internet Explorer 9, currently in development, will have complete or nearly complete support for all CSS 3 selectors including border-radius and many other properties SONY VAIO VGN-FZ480E Battery ,

faster JavaScript, embedded ICC v2 or v4 color profiles, and hardware accelerated rendering using Direct2D and DirectWrite. Microsoft has confirmed that Web Open Font Format (WOFF) will also be supported. WOFF is "a strong favorite" for standardization by the Web Fonts Working Group of W3C SONY VAIO VGN-FZ4000 Battery .

Microsoft has continued to downplay the importance of passing the Acid3 test, but speculation that IE9 would support the SVG W3C recommendation was ignited when Microsoft announced they had joined the SVG Working Group. Support for the HTML5 video and audio tags was also promised SONY VAIO VGN-FZ31E Battery .

Some industry experts predict that Microsoft will release IE9 as a major out-of-band version that is not tied to any particular version of Windows. According to the Internet Explorer 9 Test Drive page, the system requirements for IE9 are Windows Vista SP2 (with Platform Upgrade and IE8) or Windows 7 SONY VAIO VGN-FZ31B Battery .

The final build of IE9 is expected to be released in 2011.

At MIX 10, the first IE9 Platform Preview was released, which featured support for CSS3 and SVG, a new JavaScript engine called Chakra, and a score of 55/100 on the Acid3 test (up from 20/100 for IE8) SONY VAIO VGN-FZ31J Battery .

On May 5, 2010, the second IE9 Platform Preview was released, which featured a score of 68/100 on the Acid3 test and faster performance on the WebKit SunSpider JavaScript benchmark than the first IE9 Platform Preview. On June 23, 2010, the third IE9 Platform Preview was released SONY VAIO VGN-FZ31M Battery ,

which scores 83/100 on the Acid3 test and introduced support for, , and elements and WOFF. On August 4, 2010, the fourth IE9 Platform Preview was released, which features a score of 95/100 on the Acid3 test and a faster JScript engine than the third IE9 Platform Preview SONY VAIO VGN-FZ31Z Battery .

On August 12, 2010, Microsoft announced that the IE9 Public Beta would launch on September 15, 2010 at a special event in San Francisco linked to the idea of 'beauty of the web. It was also confirmed that the browser would only function with Windows Vista and Windows 7 SONY VAIO VGN-FZ38M Battery .

On September 15, 2010, Microsoft launched the IE9 Public Beta, alongside Platform Preview 5. The sixth IE9 Platform Preview was released on October 28, 2010, and includes support for CSS3 2D transforms and HTML5 semantic elements. The seventh IE9 Platform Preview was released on November 17, 2010, and features better JScript performance SONY VGP-BPS8 Battery .

On February 10, 2011, the IE9 Release Candidate was released, featuring improved performance, a tracking protection feature, a refined UI, support for more web standards, and other improvements SONY VGP-BPS13/S Battery .

Internet Explorer has been designed to view a broad range of web pages and to provide certain features within the operating system, including Microsoft Update. During the heyday of the browser wars, Internet Explorer superseded Netscape only when it caught up technologically to support the progressive features of the time SONY VGP-BPS13A/B Battery .

Standards support

Internet Explorer, using the Trident layout engine:

  • supports HTML 4.01, CSS Level 1, XML 1.0, and DOM Level 1, with minor implementation gaps SONY VGP-BPS13B/B Battery.
  • fully supports XSLT 1.0 as well as an obsolete Microsoft dialect of XSLT often referred to as WD-xsl, which was loosely based on the December 1998 W3C Working Draft of XSL. Support for XSLT 2.0 lies in the future: semi-official Microsoft bloggers have indicated that development is underway, but no dates have been announced SONY VGP-BPS13A/S Battery .
  • partially supports CSS Level 2 and DOM Level 2, with major implementation gaps and conformance issues. Almost full conformance to CSS 2.1 has been added in the Internet Explorer 8 release.
  • supports XHTML in Internet Explorer 9 (Trident version 5.0). Prior versions can render XHTML documents authored with HTML compatibility principles and served with a text/html MIME-type SONY VGP-BPS13AS Battery .
  • fully supports SVG in Internet Explorer 9 (Trident version 5.0).

Internet Explorer uses DOCTYPE sniffing to choose between standards mode and a "quirks mode" in which it deliberately mimicks nonstandard behaviors of old versions of MSIE for HTML and CSS rendering on screen (Internet Explorer always uses standards mode for printing). It also provides its own dialect ofECMAScript called JScript Dell Inspiron 1320n Battery .

Internet Explorer had been subjected to criticism by W3C over its limited support for SVG promoted by W3C.

Non-standard extensions

Internet Explorer has introduced an array of proprietary extensions to many of the standards, including HTML, CSS, and the DOMDell Inspiron 1464 Battery .

This has resulted in a number of web pages that appear broken in standards-compliant web browsers and has introduced the need for a "quirks mode" to allow for rendering improper elements meant for Internet Explorer in these other browsers Dell Inspiron 1564 Battery .

Internet Explorer has introduced a number of extensions to JScript that have been adopted by other browsers. These include the innerHTML property, which returns the HTML string within an element; the XMLHttpRequest object, which allows the sending of HTTP request and receiving of HTTP response Dell Inspiron 1764 Battery ;

and the designMode attribute of the contentDocument object, which enables rich text editing of HTML documents. Some of these functionalities were not possible until the introduction of the W3C DOM methods. Its Ruby character extension to HTML is also accepted as a module in W3C XHTML 1.1, though it is not found in all versions of W3C HTML Dell Studio 1450 Battery .

Microsoft submitted several other features of IE for consideration by the W3C for standardization. These include the 'behavior' CSS property, which connects the HTML elements with JScript behaviors (known as HTML Components, HTC) Dell Studio 1457 Battery ;

HTML+TIME profile, which adds timing and media synchronization support to HTML documents (similar to the W3C XHTML+SMIL), and the VML vector graphicsfile format. However, all were rejected, at least in their original forms. VML was, however, subsequently combined with PGML (proposed by Adobe and Sun) Dell Latitude D610 Battery ,

resulting in the W3C-approved SVG format, currently one of the few vector image formats being used on the web, and which IE is now virtually unique in not supporting.

Other non-standard behaviors include Toshiba NB100 Battery :

support for vertical text, but in a syntax different from W3C CSS3 candidate recommendation, support for a variety of image effects and page transitions, which are not found in W3C CSS, support for obfuscated script code, in particular JScript.Encode(). Support for embedding EOT fonts in web pages Toshiba Satellite M65 battery .

Favicon

The favicon (short for "favorites icon") introduced by Internet Explorer is now also supported and extended in other browsers. It allows web pages to specify a 16-by-16 pixel image for use in bookmarks Toshiba Satellite M60 battery .

In IE, support was, and still is, provided only for the native Windows ICO format; in other browsers it has now been extended to other types of images such as PNG and GIF.

Usability and accessibility

The "quick tabs" feature available inInternet Explorer 8 Dell Latitude D830 Battery

Internet Explorer makes use of the accessibility framework provided in Windows. Internet Explorer is also a user interface for FTP, with operations similar to that of Windows Explorer. Pop-up blocking and tabbed browsing were added respectively in Internet Explorer 6 and Internet Explorer 7 Dell Latitude D620 Battery .

Tabbed browsing can also be added to older versions by installing MSN Search Toolbar or Yahoo Toolbar.

Cache

Internet Explorer caches visited content in the Temporary Internet Files folder to allow quicker access (or offline access) to previously visited pages Dell Inspiron Mini 10 Battery .

The content is indexed in a database file, known as Index.dat. Multiple Index.dat files exist which index different content—visited content, web feeds, visitedURLs, cookies, etc.

Prior to IE7, clearing the cache used to clear the index but the files themselves were not reliably removed, posing a potential security and privacy risk Sony VGN-FW11S Battery .

In IE7 and later, when the cache is cleared, the cache files are more reliably removed, and the index.dat file is overwritten with null bytes.

Group Policy

Internet Explorer is fully configurable using Group Policy Sony VGN-FW11M Battery .

Administrators of Windows Server domains can apply and enforce a variety of settings that affect the user interface (such as disabling menu items and individual configuration options), as well as underlying security features such as downloading of files, zone configuration, per-site settings, ActiveX control behavior and others Sony VGN-FW139E/H battery .

Policy settings can be configured for each user and for each machine. Internet Explorer also supports Integrated Windows Authentication.

Architecture

The architecture of IE8. Previous versions had a similar architecture, except that both tabs and the UI were within the same process. Consequently, each browser window could have only one "tab process" Dell Latitude E5400 Battery .

Internet Explorer uses a componentized architecture built on the Component Object Model (COM) technology. It consists of several major components, each of which is contained in a separate Dynamic-link library (DLL) and exposes a set of COM programming interfaces hosted by the Internet Explorer main executable, iexplore.exe:

  • WinInet.dll is the protocol handler for HTTP, HTTPS and FTP. It handles all network communication over these protocols.
  • URLMon.dll is responsible for MIME-type handling and download of web content, and provides a thread-safe wrapper around WinInet.dll and other protocol implementations Dell Latitude E4200 Battery .
  • MSHTML.dll houses the Trident rendering engine introduced in Internet Explorer 4, which is responsible for displaying the pages on-screen and handling the Document Object Model of the web pages. MSHTML.dll parses the HTML/CSS file and creates the internal DOM tree representation of it Dell Inspiron 300M Battery .
  • It also exposes a set of APIs for runtime inspection and modification of the DOM tree. The DOM tree is further processed by a layout engine which then renders the internal representation on screen.
  • IEFrame.dll contains the user interface and window of IE in Internet Explorer 7 and above Dell Vostro A840 Battery .
  • ShDocVw.dll provides the navigation, local caching and history functionalities for the browser.
  • BrowseUI.dll is responsible for the browser user interface, including the browser chrome, which houses all the menus and toolbars Dell Studio 1737 battery .

Internet Explorer does not include any native scripting functionality. Rather, MSHTML.dll exposes an API that permit a programmer to develop a scripting environment to be plugged-in and to access the DOM tree. Internet Explorer 8 includes the bindings for the Active Scripting engine Dell Inspiron E1505 battery ,

which is a part ofMicrosoft Windows and allows any language implemented as an Active Scripting module to be used for client-side scripting. By default, only the JScript andVBScript modules are provided; third party implementations like ScreamingMonkey (for ECMAScript 4 support) can also be used Dell RM791 battery .

Microsoft also makes available the Microsoft Silverlight runtime that allows CLI languages, including DLR-based dynamic languages like IronPython and IronRuby, to be used for client-side scripting.

Internet Explorer 8 introduces some major architectural changes, called Loosely Coupled IE (LCIE) Dell XPS M1530 battery .

LCIE separates the main window process (frame process) from the processes hosting the different web applications in different tabs (tab processes). A frame process can create multiple tab processes, each of which can be of a different integrity level; each tab process can host multiple web sites Dell XPS M2010 battery .

The processes use asynchronous Inter-Process Communication to synchronize themselves. Generally, there will be a single frame process for all web sites. In Windows Vista with Protected Mode turned on, however, opening privileged content (such as local HTML pages) will create a new tab process as it will not be constrained by Protected Mode Acer Aspire One battery .

Extensibility

Internet Explorer exposes a set of Component Object Model (COM) interfaces that allow other components to extend the functionality of the browser. Extensibility is divided into two types: Browser extensibility and Content extensibility Toshiba Satellite P10 Battery .

The browser extensibility interfaces can be used to plug in components to add context menu entries, toolbars, menu items or Browser Helper Objects (BHO). BHOs are used to extend the feature set of the browser, whereas the other extensibility options are used to expose the feature in the UI SONY VGN-FZ210CE Battery .

Content extensibility interfaces are used by different content-type handlers to add support for non-native content formats. BHOs not only have unrestricted access to the Internet Explorer DOM and event model, they also can access the filesystem, registry and other OS components Dell Precision M70 Battery .

Content extensibility can be either in terms of Active Documents (Doc Objects) (e.g., SVG or MathML) or ActiveX controls.ActiveX controls are used for content handlers that render content embedded within an HTML page (e.g., Adobe Flash or Microsoft Silverlight) Toshiba Satellite L305 Battery .

Doc objects are used when the content type won't be embedded in HTML (e.g., Microsoft Word, PDF orXPS). In fact, the Trident rendering engine is itself exposed as a Doc object, so HTML in itself is treated as an Active Document Toshiba Satellite T4900 Battery .

Internet Explorer add-on components run with the same privileges as the browser itself, unlike client-side scripts that have a very limited set of privileges. Add-ons can be installed either locally, or directly by a web site. Since the add-ons have a more privileged access to the system, malicious add-ons can and have been used to compromise the security of the system Toshiba PA3399U-2BRS battery .

Internet Explorer 6 Service Pack 2 onwards provide various safeguards against this, including an Add-onManager for controlling ActiveX controls and Browser Helper Objects and a "No Add-Ons" mode of operation as well as greater restrictions on sites installing add-ons Toshiba Satellite A200 Battery .

Internet Explorer itself can be hosted by other applications via a set of COM interfaces. This can be used to embed the browser functionality inside the application. Also, the hosting application can choose to host only the MSHTML.dll rendering engine, rather than the entire browser Toshiba Satellite 1200 Battery .

Security

Internet Explorer uses a zone-based security framework that groups sites based on certain conditions, including whether it is an Internet- or intranet-based site as well as a user-editable whitelist. Security restrictions are applied per zone; all the sites in a zone are subject to the restrictions Toshiba Satellite M300 Battery .

Internet Explorer 6 SP2 onwards uses the Attachment Execution Service of Microsoft Windows to mark executable files downloaded from the Internet as being potentially unsafe. Accessing files marked as such will prompt the user to make an explicit trust decision to execute the file, as executables originating from the Internet can be potentially unsafe SONY VGP-BPS13A/Q Battery .

This helps in preventing accidental installation of malware.

Internet Explorer 7 introduced the phishing filter, that restricts access to phishing sites unless the user overrides the decision. With version 8, it also blocks access to sites known to host malware. Downloads are also checked to see if they are known to be malware-infected SONY VGP-BPS13A/Q Battery .

In Windows Vista, Internet Explorer by default runs in what is called Protected Mode, where the privileges of the browser itself are severely restricted—it cannot make any system-wide changes. One can optionally turn this mode off but this is not recommendedSONY VGP-BPS13B/Q Battery .

This also effectively restricts the privileges of any add-ons. As a result, even if the browser or any add-on is compromised, the damage the security breach can cause is limited.

Patches and updates to the browser are released periodically and made available through the Windows Update service, as well as through Automatic Updates SONY VGP-BPS13B/Q Battery .

Although security patches continue to be released for a range of platforms, most feature additions and security infrastructure improvements are only made available on operating systems which are in Microsoft's mainstream support phase SONY VGP-BPS13/Q Battery .

On December 16, 2008, Trend Micro recommended users switch to rival browsers until an emergency IE patch was released to fix a potential security risk which "could allow outside users to take control of a person's computer and steal their passwords". Microsoft representatives countered this recommendation, claiming that "0.02% of internet sites" were affected by the flaw SONY VGP-BPS13/Q Battery .

On December 17, 2008, a fix to the security problem above became available, with the release of the Security Update for Internet Explorer KB960714, which is available from Microsoft Windows Update's webpage. Microsoft has said that this update fixes the security risk found by Trend Micro the previous day SONY VGP-BPS21A/B Battery .

Security vulnerabilities

Internet Explorer has been subjected to many security vulnerabilities and concerns: Much of the spyware, adware, and computer viruses across the Internet are made possible by exploitable bugs and flaws in the security architecture of Internet Explorer SONY VGP-BPS21/S Battery ,

sometimes requiring nothing more than viewing of a malicious web page in order to install themselves. This is known as a "drive-by install". There are also attempts to trick the user into installing malicious software by misrepresenting the software's true purpose in the description section of an ActiveX security alert SONY VGP-BPS21B Battery .

A number of security flaws affecting IE originated not in the browser itself, but ActiveX-based add-ons used by it. Because the add-ons have the same privilege as IE, the flaws can be as critical as browser flaws. This has led to the ActiveX-based architecture being criticized for being fault-prone SONY VGP-BPS21A Battery .

By 2005, some experts maintained that the dangers of ActiveX have been overstated and there were safeguards in place. In 2006, new techniques using automated testing found more than a hundred vulnerabilities in standard Microsoft ActiveX components SONY VGP-BPS21 Battery .

Security features introduced in then recently released Internet Explorer 7 mitigated some of these vulnerabilities.

Internet Explorer in 2008 had a number of published security vulnerabilities. According to research done by security research firm Secunia, Microsoft did not respond as quickly as its competitors in fixing security holes and making patches available Sony VGP-BPS21A/B Battery .

The firm also reported 366 vulnerabilities in ActiveX controls, an increase from the prior year.

According to the latest information, Secunia reports that IE6 has 24 known unpatched vulnerabilities, IE7 has 11, and IE8 has 4. The most severe unpatched Secunia advisories affecting Microsoft Internet Explorer 6.x, 7.x, and 8 Sony VGP-BPS21/S Battery .

x with all vendor patches applied, are all rated Extremely critical. The oldest known unpatched vulnerabilities for IE6, IE7, and IE8 date from November 7, 2003, June 6, 2006, and February 26, 2007 respectively Sony VGP-BPS21A Battery .

According to the latest information, security research firm SecurityFocus reports that IE6 has 396 known unpatched vulnerabilities, IE7 has 22, and IE8 has 25. The oldest known unpatched vulnerabilities for IE6, IE7, and IE8 date from November 20, 2000, May 17, 2007, and April 11, 2009 respectively Sony VGP-BPS21 Battery .

Internet Explorer has been criticized by one Chris Evan for having a known security vulnerability which could allow information disclosure to remain unfixed for at least 600 days. Microsoft says that it had known about this vulnerability but it was of very low severity as the victim web site must be configured in a special way for this attack to be feasible at all Sony Vaio PCG-5G2L Battery .

In December 2010, researchers have been able to bypass the "Protected Mode" feature in Internet Explorer.

Vulnerability exploited in attacks on U.S. firms

In an advisory on January 14, 2010, Microsoft said that attackers targeting Google and other U.S Sony Vaio PCG-5G3L Battery .

companies used software that exploits a security hole, which had already been patched, in Internet Explorer. The vulnerability affected Internet Explorer 6, IE7, and IE8 on Windows 7, Vista, Windows XP, Server 2003, and Server 2008 R2, as well as IE 6 Service Pack 1 on Windows 2000 Service Pack 4 Sony Vaio PCG-5J1L Battery .

The German government warned users against using Internet Explorer and recommended switching to an alternative web browser, due to the major security hole described above that was exploited in Internet Explorer. The Australian and French Government issued a similar warning a few days later Sony Vaio PCG-5K2L Battery .

The first browser they recommended was Mozilla Firefox, followed by Google Chrome.

Market adoption and usage share

Source: Median values from world wide summary table.

Internet Explorer (43.8%)

Mozilla Firefox (29.7%; Usage by version number) Sony Vaio PCG-5J2L Battery

Google Chrome (13.0%)

Safari (6.1%)

Opera (2.2%)

Mobile browsers (4.3%) Sony Vaio PCG-5K1L Battery

See also: Usage share of web browsers

The adoption rate of Internet Explorer seems to be closely related to that of Microsoft Windows, as it is the default web browser that comes with Windows. Since the integration of Internet Explorer 2.0 with Windows 95 OSR 1 in 1996, and especially after version 4.0's release, the adoption was greatly accelerated Sony Vaio PCG-6S2L Battery :

from below 20% in 1996 to about 40% in 1998 and over 80% in 2000.

A CNN article noted at the release of Internet Explorer 4: "Microsoft's Internet Explorer has made inroads and various estimates put its share of the browser market 30 to 35 percent from about 10 percent a year ago Sony Vaio PCG-6S3L Battery .

" By 2002, Internet Explorer had almost completely superseded its main rival Netscape and dominated the market with up to 95 percent market share.

After having fought and won the browser wars of the late 1990s, Internet Explorer gained almost total dominance of the browser market Sony Vaio PCG-6V1L Battery .

Having attained a peak of about 95% during 2002 and 2003, its market share has since declined at a slow but steady pace. This is mainly due to the adoption of Mozilla Firefox, which statistics indicate is currently the most significant competition Sony Vaio PCG-6W1L Battery .

Nevertheless, Internet Explorer remains the dominant web browser, with a global usage share of around 60% (though measurements vary). Usage is higher in Asia and lower in Europe.

Firefox 1.0 had surpassed Internet Explorer 5 in early 2005 with Firefox 1.0 at roughly 8 percent market share Sony Vaio PCG-6W2L Battery .

An article notes at the release of Internet Explorer 7 in October 2006 that "IE6 had the lion's share of the browser market with 77.22%. Internet Explorer 7 had climbed to 3.18%, while Firefox 2.0 was at 0.69%."

Internet Explorer 7 was released at the same time as Firefox 2.0, and overtook Firefox 1.x by November 2006, at roughly 9% market share Sony Vaio PCG-6W3L Battery .

Firefox 2.0 had overtaken 1.x by January 2007, but IE7 did not surpass IE6 until December 2007. By January 2008, their respective version market share stood at 43% IE7, 32% IE6, 16% FF2, 4% Safari 3 and both FF1.x and IE5 versions at less than half a percent Sony Vaio PCG-7111L Battery .

Approximate usage over time based on various usage share counters averaged for the year overall, or for the fourth quarter, or for the last month in the year depending on availability of reference.

According to StarCounter, which tracks internet usage data, Internet Explorer's marketshare fell below 50% in September 2010 Sony Vaio PCG-7112L Battery .

Market share history overview by year and version

Approximate usage over time based on various usage share counters averaged for the year overall, or for the fourth quarter, or for the last month in the year depending on availability of reference Sony Vaio PCG-7113L Battery .

Industry adoption

The ActiveX extension mechanism is used by many public websites and web applications, including eBay. Similarly, Browser Helper Objects are also used by many search enginecompanies and third parties for creating add-ons that access their services, such as search engine toolbars Sony Vaio PCG-7133L Battery .

Because of the use of COM, it is possible to embed web-browsing functionality in third-party applications. Hence, there are a number of Internet Explorer shells, and a number of content-centric applications like RealPlayer also use Internet Explorer's web browsing module for viewing web pages within the applications Sony Vaio PCG-7Z2L Battery .

OS compatibility

IE versions, over time, have had widely varying OS compatibility, ranging from being available for many platforms and several versions of Windows to only a few versions of Windows Sony Vaio PCG-8Y1L Battery .

Many versions of IE had some support for an older OS but stopped getting updates. The increased growth of the Internet in the 1990s and 2000s means that current browsers with small market shares have more total users than the entire market early on Sony Vaio PCG-8Y2L Battery .

For example, 90% market share in 1997 would be roughly 60 million users, but by the start of 2007 90% market share would equate to over 900 million users. The result is that later versions of IE6 had many more users in total than all the early versions put together Sony Vaio PCG-8Z1L Battery .

The release of IE7 at the end of 2006 resulted in a collapse of IE6 market share; by February 2007, market version share statistics showed IE6 at about 50% and IE7 at 29%. Regardless of the actual market share, the most compatible version (across operating systems) of IE was 5.x Sony Vaio PCG-8Z2L Battery .

which had Mac OS 9 and Mac OS X, Unix, and most Windows versions available and supported for a short period in the late 1990s (although 4.x had a more unified codebase across versions). By 2007, IE had much narrower OS support, with the latest versions supporting only Windows XP Service Pack 2 and above Sony VAIO PCG-5G2L Battery .

Internet Explorer 5.0, 5.5, 6.0, and 7.0 (Experimental) have also been unofficially ported to the Linux operating system from the project IEs4Linux.

* Internet Explorer 6 SP2 is only available as part of Windows XP SP2 or Windows Server 2003 SP1 or SP2 Sony VAIO PCG-5G3L Battery .
** The version of Internet Explorer included with Windows 95 varied by OSR release; 2.0 was included with OSR1, 3.0 was included with OSR2, and 4.0 was included with OSR2.5.
*** No native support, but possible with third-party "Standalone" installer Sony VAIO PCG-5J1L Battery .
& Final version of Windows XP Service Pack 3 does not include IE7.
$ No native support, but possible with third party Standalone installer of IE6 Alpha. See also Internet Explorer Mobile. Non-desktop versions of IE have supported Windows CE also Sony VAIO PCG-5K2L Battery .
£ Internet Explorer 2.0 and 2.0.1 requires System 7.0.1 or higher. Internet Explorer 2.1 requires System 7.1 or higher.
Included Internet Explorer 3.01 in Mac OS 8.1; Internet Explorer 4.01 in Mac OS 8.5 and 8.5.1; Internet Explorer 4.5 from Mac OS 8.6 to 9.0.4; Internet Explorer 5 from Mac OS 9.1 to 9.2.2 Sony VAIO PCG-5J2L Battery .
¥ Internet Explorer 5 Macintosh Edition requires Mac OS 7.6 or higher. Internet Explorer version 5.1; 5.1.4; 5.1.5; 5.1.6 and 5.1.7 requires Mac OS 8.0 or higher or Mac OS 7.6.1 with Appearance Manager.
16 16-bit version Sony VAIO PCG-5K1L Battery

"Standalone" Internet Explorer

Early versions of Internet Explorer such as 5 had a compatibility mode to run Internet Explorer 4, though this feature was dropped (also, Internet Explorer for Mac users could still use 4.5 after installing IE 5) Sony VAIO PCG-5L1L Battery .

While Microsoft claims it is impossible to keep multiple versions of Internet Explorer on the same machine, some hackers have successfully separated several versions of Internet Explorer, making them standalone applications. These are referred to as "standalone" IEs and have included versions 3 through 7 Sony VAIO PCG-6S2L Battery .

  • Multiple IEs in Windows Web Design—The web developer Joe Maddalone who found the solution.
  • Xenocode Browser Sandbox—Xenocode application virtualization.

Microsoft has discontinued standalone installers for Internet Explorer to the general public Sony VAIO PCG-6S3L Battery .

However, there are unofficial procedures for downloading the complete install package. Internet Explorer standalone uses a feature introduced in Windows 2000 called DLL redirection to force it to load older DLLs than the ones installed on the system Sony VAIO PCG-6W1L Battery .

  • IE Collection. An installer for the standalone versions of IE8.0, IE7.0, IE6.0, IE5.51, IE5.01, IE4.01, IE3.0, IE2.01, IE1.5, and IE1.0.
  • Microsoft Support document, with instructions for downloading the entire set of installation files.

It is also possible to install Internet Explorer via Wine Sony VAIO PCG-6V1L Battery .

  • IEs4Linux automatically sets up Internet Explorer 5.0, 5.5, and 6.0 in Wine. Supporting Internet Explorer 7 is currently in development; as of August 2007, the IE7 rendering engine can be used with the IE6 user interface Sony VAIO PCG-6W1L Battery .

After Internet Explorer 7 is installed, an Internet Explorer 6 executable is still available in C:\WINDOWS\ie7, hidden by default. Launching this executable provides the user with the older IE6 interface, however web pages are rendered using the IE7 engine. The IE6 engine can be re-enabled by placing a file named "iexplore.exe.local" into the IE7 folder Sony VAIO PCG-6W2L Battery .

As an alternative to using IE standalone, Microsoft now makes available Microsoft Virtual PC images containing pre-activated copies of Windows XP with either IE 6 or IE 7 installed. Microsoft recommends this approach for web developers seeking to test their pages in the different versions of IE as the standalone versions are unsupported and may not work the same way as a properly installed copy of IE Sony VAIO PCG-6W3L Battery .

Removal

While a major upgrade of Internet Explorer can be uninstalled in a traditional way if the user has saved the original application files for installation, the matter of uninstalling the version of the browser that has shipped with an operating system remains a controversial one Sony VAIO PCG-7111L Battery .

The idea of removing a stock install of Internet Explorer from a Windows system was proposed during the United States v. Microsoft case. One of Microsoft's arguments during the trial was that removing Internet Explorer from Windows may result in system instability Sony VAIO PCG-7112L Battery .

Removing Internet Explorer does have a number of consequences. Applications that depend on libraries installed by IE will fail to function (or malfunction). The Windows help and support system will also not function due to the heavy reliance on HTML help files and components of IE Sony VAIO PCG-7113L Battery .

In versions of Windows before Vista, it is also not possible to run Microsoft's Windows Update or Microsoft Updatewith any other browser due to the service's implementation of an ActiveX control, which no other browser supports. In Windows Vista, Windows Update is implemented as a Control Panel applet Sony VAIO PCG-7Z1L Battery .

With Windows 7, Microsoft added the ability to safely remove Internet Explorer 8 from Windows. Microsoft does not allow the dependencies to be removed through this process, but the Internet Explorer executable (iexplore.exe) is removed without harming any other Windows components Sony VAIO PCG-7Z2L Battery .