Quiet PC

A quiet PC is a personal computer that makes little noise. Common uses for quiet PCs include video editing, sound mixing, home servers, and home theater PCs. A typical quiet PC uses quiet cooling and storage devices and energy-efficient parts (Dell XPS M1210 Battery) .

Like noise, the term "quiet PC" is subjective and there is currently no standard definition for a "quiet PC". However, a general definition accepted by some is that the sound emitted by such PCs should not exceed 30 dBA when measured 1 meter away from the computer (Dell Studio XPS 1340 Battery) .

In addition to the average sound pressure level, the frequency spectrum and dynamics of the sound are important in determining if the sound of the computer is noticed. Sounds with a smooth frequency spectrum (lacking audible tonal peaks), and little temporal variation are less likely to be noticed. The character and amount of other sound in the environment also affects how much sound will be noticed or masked, so a computer may be quiet with relation to a particular environment or set of users (Dell Studio XPS 1640 Battery) .

Causes of noise

The main causes of PC noise are:

• Mechanical friction noise generated by micro motors and fan bearings, as well as vibration noise from low quality chassis and improper assemblies.
• Turbulence caused by obstructions in the flow of air, such as poorly designed fan grilles and heatsinks. A lack of clearance between rotating fan blades and nearby support struts and grilles will create an audible noise, similar to how a mechanical siren operates (Dell Vostro 1710 Battery) .
• As the fan blades spin, they produce a vortex of air that trails off the edge of the blade. When the vortexes path crosses an object it may produce noise. Fan blades can be designed to reduce this problem by using special notched shapes.
• Noise generated by electrical coils or transformers used in power supplies, motherboards, video cards or LCD monitors . (ASUS EEE PC900 battery)

Noise in personal computers has been increasing with rising computing power and number of transistors on a single die (integrated circuit). More transistors of a given size use more power, which releases more heat. Faster-rotating cooling fans are one common way to remove this heat. Also, motor rotation speed for hard disc drive (HDD) and Optical disc drive (ODD) has been rising for faster data processing with technical advances in micro motors (Dell RM791 battery) .

Faster rotation (usually measured in RPM) causes higher bearing friction, thus more noise, given the same bearing technology.

The noise issue had received widespread attention with AMD's early Athlon CPUs and Intel's Pentium 4 Prescott core CPU known for its excessive heat and bundled fan noise running on high RPM. With the introduction of Home Theatre PCs (HTPC), the excessive heat and noise problem, that had been mostly confined to the overclocking and quiet computing communities, came to the attention of the general public (Sony VGP-BPS13 battery) .

The main approaches to reducing noise problems from personal computers are:

1. Reduce heat generation by using energy efficient parts - nearly all the energy used by a computer is converted into heat.
2. Improve cooling - by using more efficient cooling parts and lower friction, quieter bearings.
3. Use Soundproofing to reduce the effects of remaining noise sources (Sony VGP-BPL9 battery) .

Common noise reduction methods

• Replace heat sinks with more efficient models. This often entails the use of larger copper or aluminum heat sinks which may incorporate heat pipes.
• Replace fans with passive cooling solutions where possible, such as fans on motherboards and GPUs.
• Replace fans with low-speed, large-diameter fans with low bearing and motor noise. Larger fans can move more air per revolution than smaller fans (Sony VGP-BPL11 battery) .
• Replace the constant-speed fan in the power supply with a thermostatically controlled variable speed fan that runs at less than maximum speed, and thus runs quieter most of the time.
• Replace the power supply with a quieter model. The main considerations, from a noise-reduction point of view, in choosing a power supply are fan quality, AC/DC conversion efficiency, and how good the thermal fan speed control is at keeping the fan running slow and steady. Efficiency is important because the less heat that is produced the less work the fan has to perform (Sony VGP-BPL15 battery) .
• Replace hard drives with quieter models. Hard drives can also be replaced with laptop hard drives, with solid state devices likecompact flash or networked file systems like NFS. This reduces or eliminates this source of noise and reduces system power and cooling requirements.
• Place a damping material around hard drives (or other spinning drives) such as Sorbothane (Dell Inspiron E1505 battery) .
• Cover the case with sound insulation material such as rubber, foam or fiber mat, although this method has limited effectiveness. The material can (because of its weight) dampen case resonance, and can also absorb some high-frequency sound. Care must be taken to be sure the soundproofing does not interfere with airflow and cooling (Dell Latitude E6400 battery) .
• In energy-hungry computers, water cooling may be necessary for quiet operation. Older water pumps sometimes can make systems noisier than air-cooled, low-power computers. However, recent advances in 12v DC pump technologies have resulted in highly reduced noise levels from many pumps. In a modern watercooling system geared towards silence rather than performance, the loudest component in the computer is often the Hard Drive or Optical disc drive when performing accesses to the media (HP Pavilion dv6000 Battery) .

Low-cost methods

A number of methods exist for reducing computer noise at little or no added cost.

• Reduce CPU supply voltage ("undervolting"). Many of today's CPUs can run stably at their stock speed, or even with a slight overclock, at a reduced voltage, which reduces heat output.Underclocking can be done for the same effect, however this reduces performance and is not as effective as undervolting; all the same, underclocking may allow further undervolting (Sony Vaio VGN-FZ31S battery) .
• Power consumption is approximately proportional to V2·f, that is, it varies linearly with the clock frequency and quadratically with the voltage.This means that even a small reduction in voltage can have a large effect in power consumption. Undervolting and underclocking can also be used with chipsets and GPUs.
• Enable Cool'n'Quiet for AMD CPUs or EIST on Intel's CPUs (Sony Vaio VGN-FZ31S battery) .
• Reduce fan speed. For newer computers, the speed of fans can be varied automatically, depending on how hot certain parts of the computer get. Lowering a DC fan motor's supply voltage will reduce its speed while making it quieter and lowering the amount of air the fan moves. Doing this arbitrarily could lead to components overheating; therefore, whenever performing hardware work it is advised to monitor the temperature of system components (Hp pavilion dv6000 battery) .
• Fans with Molex connectors can be modified easily. With 3-pin fans, either fixed inline resistors or diodes, or commercial fan controllers, such as the Zalman Fanmate, can be used. Software like speedfan may allow fan speed control. Many newer motherboards support Pulse-width modulation (PWM) control, allowing the fan speed to be set in the BIOS or with software (Sony VGN-FW11S Battery) .
• Mount fans on anti-vibration mounts.
• Remove restrictive fan grills to allow easier airflow, or replace noisy fan grills with quieter versions.
• Use software such as Nero DriveSpeed to reduce the speed of optical drives.
• Isolate hard disk noise, either by using anti-vibration mounts (generally rubber or silicone grommets), or by suspending the hard disk to fully decouple it from the computer chassis by mounting it in a 5.25 inch drive bay with viscoelastic polymer mounts (Sony VGP-BPS13A/B Battery) .
• Set the hard disk's AAM value to its lowest setting. This reduces the seek noise produced by the hard drive, but also reduces performance slightly.
• Set operating system to spin down hard drives after a short time of inactivity. This may reduce a drive's life span and commonly conflicts with the OS and running programs, though it can still be useful for drives that are only used for data storage (Toshiba Satellite P10 Battery) .
• Defragment the hard drives to reduce the drive heads' need to search widely for data, also improves performance. This may not be practical or even possible with some operating systems, such as Linux, UNIX or Free BSD.
• Arrange components and cables to improve airflow. Wires hanging inside the computer can block the airflow, which can increase the temperature. They can be easily moved to the side of the case so that air can pass through more easily (SONY VAIO VGN-FZ210CE Battery) .
• Remove dust from inside the computer. Dust on computer parts will retain more heat. Fans draw in dust along with outside air, it can build up quickly inside the computer. Dust can be removed with a vacuum cleaner, gas duster or compressed air. Special anti-static vacuum cleaners should be used however to prevent electrostatic discharge (ESD). Ideally, this would be done often enough to prevent a significant amount of dust from ever building up. How frequently this would need to be performed would depend entirely on the environment in which the computer is used (Hp Pavilion dv3-1000 battery) .

Sound power and pressure measurement

Though standards do exist for measuring and reporting sound power output by such things as computer components, they are often ignored. Many manufacturers do not give sound power measurements. Some report sound pressure measurements, but those that do often do not specify how sound pressure measurements were taken. Even such basic information as measurement distance is rarely reported (Dell Precision M70 Battery) .

Without knowing how it was measured, it is not possible to verify these claims, and comparisons between such measurements (e.g. for product selection) are meaningless. Comparative reviews, which test several devices under the same conditions are more useful. Although even then, an average sound pressure level is only one factor in determining which components will be perceived as quieter (Acer Aspire One battery) .

Individual components in a quiet PC

The following are notes regarding individual components in quiet PCs.

The motherboard, CPU and video card are major energy users in a computer. Components that need less power will be easier to cool quietly. The a quiet power supply is selected to be efficient when providing enough power for the computer (Toshiba Satellite L305 Battery) .

Motherboards

Main article: Motherboards

Passively cooled northbridge chipsets help reduce noise.

A motherboard based on a chipset that uses less energy may be easier to cool quietly.

Many modern motherboard chipsets have hot northbridges (notably nForce4), which may come with active cooling, usually a small, noisy fan. Fanless heatsinks, such as the Zalman ZM-NB47J, ZM-NBF47 or the Thermalright HR-05, may be used to eliminate a noisy chipset fan (Toshiba Satellite Pro M15 Battery) .

Some motherboard manufacturers have got rid of these fans by incorporating large heatsinks or heatpipe coolers, however they still require good case airflow to remove heat. Also, motherboard voltage regulators often have heatsinks and may need airflow to ensure adequate cooling.

Motherboards can also produce coil noise.

Undervolting and underclocking generally require motherboard support.

Some motherboards can control the fan speed using software like speedfan. Most recent motherboards have built in PWM based fan control for one or two fans (Toshiba Satellite M65 battery) .

CPUs

A large copper heatsink and high flow fan provide exceptional cooling for the cooler-running Pentium 4 Northwood.

The heat output of a CPU can vary according to its brand and model - to be exact, its TDP. Intel's third revision Pentium 4, using the "Prescott" core, was infamous for being one of the hottest-running CPUs on the market. By comparison, AMD's Athlon series and the new Intel Core 2 perform better at lower clock speeds, and thus produce less heat (Toshiba Satellite T4900 Battery) .

Modern CPUs often incorporate energy saving systems, such as Cool'n'Quiet, LongHaul, and EIST. These reduce the CPU clock speed and core voltagewhen the processor is idle, thus reducing heat. The heat produced by CPUs can be further reduced by undervolting, underclocking or both (Toshiba PA3399U-2BRS battery) .

Most modern mainstream and value CPUs are made with a lower TDP to reduce heat, noise, and power consumption. Most of Intel's desktop Core 2 Duo processors have 65W TDPs, and AMD has newer processors with a TDP between 35W and 65W. Some processors come in special low power versions (Toshiba Satellite A200 Battery) .

Modern low power CPUs

Maximum TDP:

• Athlon 64 X2: 45W, 65W, 85W
• Intel Core and Core 2 series: 35W, 65W, 85W
• Intel Pentium M and Celeron M (lacks SpeedStep)
• VIA C7: 12W-20W (Fanless)
• transmeta processors
• Geode (processor): 5W, 25W
• Intel Atom: 2W, 4W, 8W
• Loongson: 1W, 5W, 7W (Fanless) (Toshiba Satellite 1200 Battery)

Video cards

Video cards can produce a significant amount of heat. A fast GPU may be the largest power consumer in a computer. For instance, 161 watts peak power consumption for an ATI Radeon HD 2900 XT 512. Because of space limitations, video card coolers often use small fans running at high speeds, making them noisy (Toshiba NB100 Battery) .

Display options for making a quiet computer include:

• Use motherboard video output - typically motherboard video takes less power than an external video card, typically at the price of lower gaming or HD video decoding performance.
• Select a video card that does not use a fan
  • many of the more efficient GPUs are available in fanless models
  • many older video cards used less power than more recent video cards, thus heatsinks or fans were often not required
• Replace the GPU cooler with a larger heatsink and possibly a larger, slower fan (Toshiba Satellite M300 Battery)
• No video card - use a terminal, thin client, USB display or desktop sharing software if display required

Power supplies

Main article: Computer power supply

PSUs are made quieter through the use of higher efficiency (which reduces waste heat and need for airflow), quieter fans, more intelligent fan controllers (ones for which the correlation between temperature and fan speed is more complex than linear), more effective heatsinks and through designs which allow air to flow through with less resistance.

For a given power supply size, more efficient supplies, such as those certified 80 plus, generate less heat (Dell INSPIRON 1525 battery) .

Selecting a power supply of appropriate wattage for the computer is important for high efficiency and minimizing heat. Power supplies are typically less efficient when lightly or heavily loaded. High wattage power supplies will typically be less efficient when lightly loaded, for instance when the computer is idle or sleeping. Most desktop computers spend most of their time lightly loaded (Dell Latitude D830 Battery) .

For example, most desktop PCs draw less than 250 watts at full load, and 200 watts or less is more typical.

Power supplies with thermally controlled fans can be made quieter by providing a cooler and/or less obstructed source of air. For instance, the power supply is in a separate compartment in the Antec P180 to keep the air supplied to the PSU cool.

The fan in a power supply can be replaced with a quieter one, although there is a risk of electric shock when doing this, and it usually voids the warranty (Dell Studio 1735 Battery) .

Fanless power supplies are available.

• Some of them are equipped with large passive heat sinks and rely on convection or case airflow to dissipate heat. It is also imperative that such fanless power supplies be installed in a case with good ventilation.
• There are also fanless DC to DC power supplies that operate like those in laptops, using an external power brick to supply DC power, which is then converted to appropriate voltages and regulated for use by the computer. These power supplies usually have lower wattage ratings (Dell Latitude D620 Battery) .

The electrical coils in power supplies can produce noise which can become noticeable in a quiet PC.

Cases

Main article: Computer case

Antec P180, with isolated chambers for more segregated airflow.

Another example of the Antec P180, this one demonstrating the use of the Scythe Ninja, a fanless CPU cooler (SONY VAIO VGN-FZ150E Battery) .

Cases designed for low noise usually include reasonably quiet fans, and often come with a relatively quiet power supply. Some cases for quiet computers incorporate heatsinks to cool components passively.

Cases that provide lots of space make it easier to quiet a PC, both by allowing for airflow and by accommodating large coolers (Sony VGN-FZ31Z Battery) .

Case airflow

Noise optimized cases like the Antec P180 and Antec P150 often have ducting and partitioning within the case to optimize airflow and thermally isolate components. For example, the P180 has the PSU mounted in the bottom of the case in an isolated partition. This design feature allows cooler air to enter the PSU, reducing the necessary airflow and accordingly, the noise output of the fan. Apple has also employed this tactic in their G5 workstations in an effort to reduce noise (SONY VAIO VGN-FZ38M Battery) .

Antec's Sonata is often considered by the mainstream to be one of the quietest PC cases; however, it has since been surpassed by the P180 and other more-advanced cases. Vents and ducts may easily be added to regular cases.

More obstructive fan grills increase pressure drop and lower airflow, necessitating higher fan speeds and more noise output. They also increase the turbulence of the flow, which causes some noise of its own (SONY VAIO VGN-FZ21m Battery) .

Cases designed to be quiet typically have wire grills or honeycombed fan grills, which perform almost as well as wire grills; both are far superior to the old style of stamped grill.

Features that facilitate neat cable management, such as brackets and space to run cables behind motherboard tray, help increase cooling efficiency (SONY VAIO VGN-FZ18m Battery) .

Air filtering

Air filters can help to prevent dust from coating heatsinks and surfaces, thereby impeding heat transfer, making fans spin faster. However the filter itself can increase noise if it restricts airflow too much, or is not cleaned, requiring a larger or faster fan to handle the pressure drop behind the filter.

Regular cleaning of air intake filters will help to keep airflow minimally restricted and keep the interior clean (SONY VAIO VGN-FZ11m Battery) .

In some cases a fine mesh intake screen is sufficient to stop most large dust particles from entering the system. These screens should be vacuumed or washed to remove dust.

Case soundproofing

The inside of a case can be lined with dampening materials to reduce noise by:

• attenuating the vibration of the case panels via extensional damping or constrained-layer damping.
• reducing the amplitude of the vibration of the case panels by increasing their mass.
• absorbing airborne noise, such as with foam (Dell Studio 1555 Battery) .

Cooling systems

Main article: Computer cooling

Heat sinks

Main article: Heat sink

Heat sinks that operate efficiently with little airflow are often used in quiet computers. Typically they are (relatively) large, and have larger spaces to allow freer airflow. Often heat pipes are used to help distribute heat. For instance, in 2007, the Scythe Ninja or the Thermalright Ultra-120 were frequently used as CPU heat sinks in quiet computers (Dell Latitude D610 Battery) .

Fans

Main article: Computer fan

A 120 mm variable speed fan.

Bearing and motor noise vary between different fan models and often between different samples of the same model.

Quiet PCs typically use larger (e.g. 120 mm) low-speed fans. Although 140 mm fans are made by some manufacturers, such as Aerocool and Yate Loon, there are very few cases or heatsinks that can use them. Fan adapters, which allow larger fans to be used in place of smaller ones, and fan brackets, like the Zalman FB123, often help when replacing small fans (Dell Vostro 1500 Battery) .

Quiet fan manufacturers include Nexus, EBM-Papst, Yate Loon and Scythe. In situations where the resistance to flow is very low, like in free-air conditions,Noctua fans also perform very well. Extensive comparative surveys have been posted by Silent PC Review and MadShrimps.

Fan controllers can be used to slow down fans and to precisely choose fan speed. Fan controllers can produce a fixed fan speed using an inline resistor or diode, or a variable speed using a potentiometer or Pulse Width Modulation (PWM) (Dell Latitude D610 Battery) .

Resistor-based fan control feeds the fan a lower voltage, while PWM fan control rapidly cycles between feeding the fan full voltage and no voltage. PWM fan control reduces rotational speed, and is the easiest and most efficient option for motherboards which have PWM fan headers. This is because PWM fans in conjunction with the motherboard chipset obtain temperature data from Digital Temperature Sensors on the CPU itself. All PWM fans are four pin, and if plugged into a conventional three pin supply will operate at full speed just like a three pin fan (Toshiba Satellite M60 battery) .

Fans can also be plugged into the power supply's 5 volt line instead of the 12 volt line (or between the two for a potential difference of 7 volts, although this cripples the fan's speed sensing) to run them at a reduced speed. Most fans will run at 5 volts once they are spinning, but may not start reliably at less than 7 V. Some simple fan controllers will only vary the fans' supply voltage between 8 V and 12 V to avoid this problem entirely. Some fan controllers start the fan at 12 V, then drop the voltage after a few seconds (SONY VAIO VGN-FZ11S Battery) .

Soft mounting fans (e.g. with rubber or silicone fan isolators) can help reduce transfer of fan vibrations to other components.

Intel has recently developed a piezoelectric fan for use in desktop PCs, which is quieter than motor fans and consumes a fraction of the power (HP Pavilion DV7 Battery) .

Watercooling

Main article: Watercooling

Watercooling is a method of heat-dissipation by transferring the heat through a conductive material which is in contact with a liquid, most often demineralised water and an additive to prevent bacterial growth and provide cosmetic effects. This heated water travels in a loop which usually contains a reservoir, radiator and pump. Recent advances in 12v DC pump technologies (for the first time specifically geared-for pc development) allow for new pumps to be both extremely powerful and extremely quiet (Dell Vostro 1400 Battery) .

Loops can be made up of any combination of these items and some aren't required such as the radiator or reservoir if alternatives methods are used. The radiator often uses one or more fans to air cool the radiator fins and dissipate the majority of the heat at this point.

The most common loop order is reservoir to pump, radiator then the watercooling block and back to the reservoir (Dell RM791 battery) .

The radiator and fan efficiency has the greatest effect on the noise level and cooling efficiency but watercooling is currently the most effective and potentially quietest methods of cooling above ambient temperatures.

There is an inherent danger in the use of water around electrical equipment and leak testing the loop is always recommended before attaching any parts to the motherboard, after all loop connections have been made. The 12v DC pump can be run using batteries or a power supply making sure no power is going to any other part of the system (SONY VAIO VGN-FZ Battery) .

Because of these risks and the use of water under pressure watercooling is a greater technical challenge to set up due to the number of components and case modification usually required.

Secondary storage

Hard drives

Main article: Hard drives

Silicone grommets in a computer case for mounting a hard drive to reduce vibration.

Previously, hard drives used ball bearing motors, but they got noisy when the rotational speed of the drive was increased to 5400 RPM or 7200 RPM. More recent desktop hard drives use fluid bearing motors. The first hard drive widely reputed to be quiet was the Seagate Barracuda ATA IV (Hp 520 battery) .

The smaller 2.5" form-factor hard drives generally vibrate less, are quieter, and use less power than the traditional 3.5" drives. On the other hand, they often have lower performance and less capacity, and cost more per gigabyte.

To minimize vibrations from a hard drive being transferred to, and amplified by, the case, hard drives can be mounted with soft rubber studs, suspended with elastics or placed on soft foam or Sorbothane (HP Pavilion dv9000 battery) .

Hard disk enclosures can also help reduce drive noise. Care must be taken to ensure that the drive gets adequate cooling. Hard disk temperatures can often be monitored by SMART software.

Solid-state storage

Flash memory

Solid-state drive

Solid-state drive (SSD) storage offers faster seek times, lower power consumption, no moving parts; making it theoretically more reliable and silent. There is scope for very high capacity drives; however, they are currently extremely expensive per GB and are fairly scarce (Dell Vostro 1000 battery) .

Compact Flash cards

A few people use Compact Flash (CF) cards for storage. Because they use IDE protocol, a simple adapter is all that is needed to connect CF cards to function as an IDE or PC Card hard disk. CF cards are also small, allowing SFF PCs to be made, produce no noise, use very little power (further reducing heat output in the AC/DC conversion in the PSU), and an insignificant amount of heat. However, they are very expensive per GB and are only available in small capacities (Dell XPS M2010 battery) .

There are also issues regarding the maximum number of writes to each sector; often specified as 100,000 write cycles. However, there are industrial grade cards which specify a higher number of erase cycles, and different file systems, or technologies such as Enhanced Write Filter can reduce the writes to the card. Also, CF cards will fail gradually, so it will be easy to notice before any significant amount of data are lost, unlike the possible immediate failure of HDDs (Dell XPS M1530 battery) .

Due to their small capacities they are easy to back up entirely, and often have 10 year or even lifetime warranties.

Windows minimization projects such as Winimize (Windows 98, less than 20MB) and Linux projects such as Puppy Linux mean that running an OS in small capacity, cheap compact flash card is possible. Because they have many OS components removed, they are less prone to viruses and other malware (Dell Studio 1737 battery) .

The sustained transfer rate of current CF cards is a maximum of around 25 MB/s, compared to an average of around 70 MB/s for modern hard drives. However, the speed of flash memory is increasing at a faster rate than that of hard drives, and they have minimal seek times compared to hard drives, which increases the speed of loading many small files, and makes the PC seem more responsive as most operations performed by the OS include small files (Dell Inspiron 300M Battery) .

Due to the fast seek times CF cards also don't show the effects of file system fragmentation like hard drives do.

Newer CF cards support faster transfer protocols like DMA. It is possible to use a Compact Flash card for storing only information that isn't changed very often, such as music, videos and binary executables, while storing the small configuration files and other frequently modified data on a small hard drive or i-RAM (Dell Studio 1735 Battery) .

USB flash drives

Main article: USB flash drives

Where a motherboard supports booting from USB drives, they can be used in a similar fashion to CF cards to run the OS. With some Linux distributions, it is not much harder than using a CF card. As they both use flash memory, they have the same advantages and disadvantages, however speed is limited by the USB bus (Dell Studio 1555 Battery) .

Gigabyte i-RAM

The i-RAM is a solid-state disk which has four DIMM slots to allow regular PC RAM to be used like a disk. It is much faster than a hard disk, does not have the write cycle limitations of flash memory, however it requires power continuously in order to maintain its contents (from standby power or a battery when the system is off), uses more power than many laptop hard drives, has maximum capacity of 4 GiB, and is expensive (Dell Latitude E6400 battery) .

Problems and solutions

All forms of affordable solid-state storage offer relatively small capacity. They can be used as main storage for tasks which do not use large amounts of data or large programs, such as web browsing or word processing. Larger files and programs can be stored on a secondary hard drive which is only accessed when needed. Keeping the OS, often accessed files, and smaller programs on a solid-state drive means that the hard drives can be powered down much of the time (Sony Vaio VGN-FZ61B battery) .

Network-attached storage, or NAS, is another alternative, allowing loud hard drives to be stored remotely.

Small USB drives or CF cards can be used to make the process of network booting easier also.

Optical drives

Optical drives can be slowed down by software to quiet them, such as Nero DriveSpeed, or emulated by virtual drive programs such as Daemon Tools to eliminate their noise entirely. Notebook optical drives can be used, which tend to be quieter, however this may be because they tend to run slower (typically 24x CD speed, 8x DVD speed). Some DVD drives have a feature, commonly calledRiplock, which reduces drive noise by slowing the drive during video playback (Acer Aspire One battery) .

External components

Laptops

Main article: Laptops

Laptop computers typically do not have power supply fans or video card fans, and they use smaller hard drives. They also use many lower power components. However, laptop CPU coolers are usually smaller, so may be noisier than their desktop counterparts. Limited space, limited access and proprietary components make silencing laptops more difficult (HP Pavilion DV4 Battery) .

A few laptops do not use cooling fans, for instance the Dell Latitude X1, Panasonic Toughbook W5 and T5, Fujitsu Lifebook P7120. Also, some netbooks, such as the Dell Mini 9, 10 and 12 do not have fans. The Mini 9 used SSD rather than a hard disk. The OLPC XO-1 has no internal moving parts .

Monitors

Main article: Computer display

CRT monitors can produce coil noise, as can the external power supply for an LCD monitor or the voltage converter for the monitor's backlight (SONY VAIO VGN-FZ460E Battery) .

LCD monitors tend to produce the least noise (whine) from when at full brightness. Reducing brightness using the video card does not introduce whine, but may reduce color accuracy.An LCD monitor with an external power supply tucked out of the way will produce less noticeable noise than one with the power supply built into the screen housing (Dell Vostro A90 Battery) .

Printers

Main article: Computer printer

Dot matrix and daisy wheel printers are often noisy, and soundproofed boxes or cabinets can be used to reduce the noise. Another solution is to locate the printer away from the immediate work area or in another room, especially if it can be controlled through a local area network (Dell Vostro A860 Battery) .

Green computing

Green computing or green IT, refers to environmentally sustainable computing or IT. In the article Harnessing Green IT: Principles and Practices, San Murugesan defines the field of green computing as "the study and practice of designing, manufacturing, using, and disposing of computers, servers, and associated subsystems—such as monitors, printers, storage devices, and networking and communications systems—efficiently and effectively with minimal or no impact on the environment (Dell XPS M1210 Battery) ."

The goals of green computing are similar to green chemistry; reduce the use of hazardous materials, maximize energy efficiency during the product's lifetime, and promote the recyclability or biodegradability of defunct products and factory waste. Research continues into key areas such as making the use of computers as energy-efficient as possible, and designing algorithms and systems for efficiency-related computer technologies (Dell Studio XPS 1340 Battery) .

Origins

In 1992, the U.S. Environmental Protection Agency launched Energy Star, a voluntary labeling program which is designed to promote and recognize energy-efficiency in monitors, climate control equipment, and other technologies. This resulted in the widespread adoption of sleep mode among consumer electronics (Dell Studio XPS 1640 Battery) .

The term "green computing" was probably coined shortly after the Energy Star program began; there are several USENET posts dating back to 1992 which use the term in this manner.Concurrently, the Swedish organization TCO Development launched the TCO Certification program to promote low magnetic and electrical emissions from CRT-based computer displays; this program was later expanded to include criteria on energy consumption, ergonomics, and the use of hazardous materials in construction (Dell Vostro 1710 Battery) .

Regulations and industry initiatives

The Organisation for Economic Co-operation and Development (OECD) has published a survey of over 90 government and industry initiatives on "Green ICTs", i.e. information and communication technologies, the environment and climate change. The report concludes that initiatives tend to concentrate on the greening ICTs themselves rather than on their actual implementation to tackle global warming and environmental degradation (ASUS EEE PC900 battery) .

In general, only 20% of initiatives have measurable targets, with government programs tending to include targets more frequently than business associations.

Government

Many governmental agencies have continued to implement standards and regulations that encourage green computing. The Energy Star program was revised in October 2006 to include stricter efficiency requirements for computer equipment, along with a tiered ranking system for approved products (Dell RM791 battery) .

Some efforts place responsibility on the manufacturer to dispose of the equipment themselves after it is no longer needed; this is called the extended producer responsibility model. The European Union's directives 2002/95/EC (Restriction of Hazardous Substances Directive), on the reduction of hazardous substances, and 2002/96/EC (Waste Electrical and Electronic Equipment Directive) on waste electrical and electronic equipment required the substitution of heavy metals and flame retardants like Polybrominated biphenyl and Polybrominated diphenyl ethers in all electronic equipment put on the market starting on July 1, 2006 (Sony VGP-BPS13 battery) .

The directives placed responsibility on manufacturers for the gathering and recycling of old equipment.

There are currently 26 US States that have established state-wide recycling programs for obsolete computers and consumer electronics equipment. The statutes either impose an "advance recovery fee" for each unit sold at retail, or require the manufacturers to reclaim the equipment at disposal (Sony VGP-BPL9 battery).

Industry

Climate Savers Computing Initiative (CSCI) is an effort to reduce the electric power consumption of PCs in active and inactive states.[9] The CSCI provides a catalog of green products from its member organizations, and information for reducing PC power consumption. It was started on 2007-06-12. The name stems from the World Wildlife Fund's Climate Savers program, which was launched in 1999.[10] The WWF is also a member of the Computing Initiative (Sony VGP-BPL11 battery) .

The Green Electronics Council offers the Electronic Product Environmental Assessment Tool (EPEAT) to assist in the purchase of "greener" computing systems. The Council evaluates computing equipment on 51 criteria - 23 required and 28 optional - that measure a product's efficiency and sustainability attributes. Products are rated Gold, Silver or Bronze depending on how many optional criteria they meet (Sony VGP-BPL15 battery) .

On 2007-01-24, President George W. Bush issued Executive Order 13423, which requires all United States Federal agencies to use EPEAT when purchasing computer systems.

The Green Grid is a global consortium dedicated to advancing energy efficiency in data centers and business computing ecosystems. It was founded in February 2007 by several key companies in the industry – AMD, APC, Dell, HP, IBM, Intel, Microsoft, Rackable Systems, SprayCool, Sun Microsystems and VMware (Dell Inspiron E1505 battery) .

The Green Grid has since grown to hundreds of members, including end users and government organizations, all focused on improving data center efficiency.

The Green500 list rates supercomputers by energy efficiency (megaflops/watt, encouraging a focus on efficiency rather than absolute performance (Dell Latitude E6400 battery) .

Green Comm Challenge is an organization that promotes the development of energy conservation technology and practices in the field of Information and Communications Technology (ICT). Green Comm Challenge achieved worldwide notoriety in 2007, when it enlisted as one of the challengers in the 33rd edition of the America's Cup, an effort meant to show how researchers, technologists and entrepreneurs from around the world can be brought together by an exciting vision: building the ultimate renewable energy machine, a competitive America’s Cup boat (HP Pavilion dv6000 Battery) .

Approaches to green computing

In the article Harnessing Green IT: Principles and Practices, San Murugesan defines the field of green computing as "the study and practice of designing, manufacturing, using, and disposing of computers, servers, and associated subsystems—such as monitors, printers, storage devices, and networking and communications systems—efficiently and effectively with minimal or no impact on the environment (Sony Vaio VGN-FZ31S battery) ."

Murugesan lays out four paths along which he believes the environmental effects of computing should be addressed: Green use, green disposal, green design, and green manufacturing.

Modern IT systems rely upon a complicated mix of people, networks and hardware; as such, a green computing initiative must cover all of these areas as well (Sony Vaio VGN-FZ31S battery) .

A solution may also need to address end user satisfaction, management restructuring, regulatory compliance, and return on investment (ROI). There are also considerable fiscal motivations for companies to take control of their own power consumption; "of the power management tools available, one of the most powerful may still be simple, plain, common sense (Hp pavilion dv6000 battery) ."

Product longevity

Gartner maintains that the PC manufacturing process accounts for 70 % of the natural resources used in the life cycle of a PC. Therefore, the biggest contribution to green computing usually is to prolong the equipment's lifetime. Another report from Gartner recommends to "Look for product longevity, including upgradability and modularity (Sony VGN-FW11S Battery) ."

For instance, manufacturing a new PC makes a far bigger ecological footprint than manufacturing a new RAM module to upgrade an existing one, a common upgrade that saves the user having to purchase a new computer.

Software and deployment optimization

Algorithmic efficiency

Main article: Algorithmic efficiency

The efficiency of algorithms has an impact on the amount of computer resources required for any given computing function and there are many efficiency trade-offs in writing programs (Sony VGP-BPS13B/B Battery) .

As computers have become more numerous and the cost of hardware has declined relative to the cost of energy, the energy efficiency and environmental impact of computing systems and programs has received increased attention. A study by Alex Wissner-Gross, a physicist at Harvard, estimated that the average Google search released 7 grams of carbon dioxide (CO?). However, Google disputes this figure, arguing instead that a typical search produces only 0.2 grams of CO? (Sony VGP-BPS13A/B Battery) .

Resource allocation

Main article: Resource allocation

Algorithms can also be used to route data to data centers where electricity is less expensive. Researchers from MIT, Carnegie Mellon University, and Akamai have tested an energy allocation algorithm that successfully routes traffic to the location with the cheapest energy costs (Toshiba Satellite P10 Battery) .

The researchers project up to a 40 percent savings on energy costs if their proposed algorithm were to be deployed. Strictly speaking, this approach does not actually reduce the amount of energy being used; it only reduces the cost to the company using it. However, a similar strategy could be used to direct traffic to rely on energy that is produced in a more environmentally friendly or efficient way (SONY VAIO VGN-FZ210CE Battery) .

A similar approach has also been used to cut energy usage by routing traffic away from data centers experiencing warm weather; this allows computers to be shut down to avoid using air conditioning.

Larger server centers are sometimes located where energy and land are inexpensive and readily available. Local availability of renewable energy, climate that allows outside air to be used for cooling, or locating them where the heat they produce may be used for other purposes could be factors in green siting decisions (Hp Pavilion dv3-1000 battery) .

Virtualization

Main article: Platform virtualization

See also: Comparison of platform virtual machines

Computer virtualization refers to the abstraction of computer resources, such as the process of running two or more logical computer systems on one set of physical hardware. The concept originated with the IBM mainframe operating systems of the 1960s, but was commercialized for x86-compatible computers only in the 1990s (Dell Precision M70 Battery) .

With virtualization, a system administrator could combine several physical systems into virtual machines on one single, powerful system, thereby unplugging the original hardware and reducing power and cooling consumption. Virtualization can assist in distributing work so that servers are either busy, or put in a low power sleep state. Several commercial companies and open-source projects now offer software packages to enable a transition to virtual computing (Acer Aspire One battery) .

Intel Corporation and AMD have also built proprietary virtualization enhancements to the x86 instruction set into each of their CPU product lines, in order to facilitate virtualized computing.

Terminal servers

Main article: Terminal server

Terminal servers have also been used in green computing. When using the system, users at a terminal connect to a central server; all of the actual computing is done on the server, but the end user experiences the operating system on the terminal (Toshiba Satellite L305 Battery) .

These can be combined with thin clients, which use up to 1/8 the amount of energy of a normal workstation, resulting in a decrease of energy costs and consumption. There has been an increase in using terminal services with thin clients to create virtual labs. Examples of terminal server software include Terminal Services for Windows and the Linux Terminal Server Project (LTSP) for the Linux operating system (Toshiba Satellite Pro M15 Battery) .

Power management

Main article: Power management

The Advanced Configuration and Power Interface (ACPI), an open industry standard, allows an operating system to directly control the power-saving aspects of its underlying hardware (Toshiba Satellite M65 battery) .

This allows a system to automatically turn off components such as monitors and hard drives after set periods of inactivity. In addition, a system may hibernate, where most components (including the CPU and the system RAM) are turned off. ACPI is a successor to an earlier Intel-Microsoft standard called Advanced Power Management, which allows a computer's BIOS to control power management functions (Toshiba Satellite T4900 Battery) .

Some programs allow the user to manually adjust the voltages supplied to the CPU, which reduces both the amount of heat produced and electricity consumed. This process is called undervolting. Some CPUs can automatically undervolt the processor depending on the workload; this technology is called "SpeedStep" on Intel processors, "PowerNow!"/"Cool'n'Quiet" on AMD chips, LongHaul on VIA CPUs, and LongRun with Transmeta processors (Toshiba PA3399U-2BRS battery) .

Operating system support

The dominant desktop operating system, Microsoft Windows, has included limited PC power management features since Windows 95. These initially provided for stand-by (suspend-to-RAM) and a monitor low power state. Further iterations of Windows added hibernate (suspend-to-disk) and support for the ACPI standard (Toshiba Satellite A200 Battery) .

Windows 2000 was the first NT based operating system to include power management. This required major changes to the underlying operating system architecture and a new hardware driver model. Windows 2000 also introduced Group Policy, a technology which allowed administrators to centrally configure most Windows features (Toshiba Satellite 1200 Battery) .

However, power management was not one of those features. This is probably because the power management settings design relied upon a connected set of per-user and per-machine binary registry values, effectively leaving it up to each user to configure their own power management settings (Toshiba NB100 Battery) .

This approach, which is not compatible with Windows Group Policy, was repeated in Windows XP. The reasons for this design decision by Microsoft are not known, and it has resulted in heavy criticism Microsoft significantly improved this in Windows Vista by redesigning the power management system to allow basic configuration by Group Policy (Toshiba Satellite M300 Battery) .

The support offered is limited to a single per-computer policy. The most recent release, Windows 7 retains these limitations but does include refinements for more efficient user of operating system timers, processor power management, and display panel brightness. The most significant change in Windows 7 is in the user experience. The prominence of the default High Performance power plan has been reduced with the aim of encouraging users to save power (Dell INSPIRON 1525 battery) .

There is a significant market in third-party PC power management software offering features beyond those present in the Windows operating system. Most products offer Active Directory integration and per-user/per-machine settings with the more advanced offering multiple power plans, scheduled power plans, anti-insomnia features and enterprise power usage reporting (Toshiba NB100 Battery) .

Power supply

Desktop computer power supplies (PSUs) are generally 70–75% efficient,dissipating the remaining energy as heat. An industry initiative called 80 PLUS certifies PSUs that are at least 80% efficient; typically these models are drop-in replacements for older, less efficient PSUs of the same form factor. As of July 20, 2007, all new Energy Star 4.0-certified desktop PSUs must be at least 80% efficient (Dell Latitude D830 Battery) .

Storage

Smaller form factor (e.g. 2.5 inch) hard disk drives often consume less power per gigabyte than physically larger drives. Unlike hard disk drives, solid-state drives store data in flash memory or DRAM. With no moving parts, power consumption may be reduced somewhat for low capacity flash based devices (Dell Studio 1735 Battery) .

In a recent case study, Fusion-io, manufacturers of the world's fastest Solid State Storage devices, managed to reduce the carbon footprint and operating costs of MySpace data centers by 80% while increasing performance speeds beyond that which had been attainable via multiple hard disk drives in Raid 0. In response, MySpace was able to permanently retire several of their servers, including all their heavy-load servers, further reducing their carbon footprint (Dell Latitude D620 Battery) .

As hard drive prices have fallen, storage farms have tended to increase in capacity to make more data available online. This includes archival and backup data that would formerly have been saved on tape or other offline storage. The increase in online storage has increased power consumption. Reducing the power consumed by large storage arrays, while still providing the benefits of online storage, is a subject of ongoing research (SONY VAIO VGN-FZ150E Battery) .

Video card

A fast GPU may be the largest power consumer in a computer.

Energy efficient display options include:

No video card - use a shared terminal, shared thin client, or desktop sharing software if display required.

Use motherboard video output - typically low 3D performance and low power (Sony VGN-FZ31Z Battery) .

Select a GPU based on low idle power, average wattage or performance per watt.

Display

CRT monitors typically use more power than LCD monitors. They also contain significant amounts of lead. LCD monitors typically use a cold-cathode fluorescent bulb to provide light for the display. Some newer displays use an array of light-emitting diodes (LEDs) in place of the fluorescent bulb, which reduces the amount of electricity used by the display (SONY VAIO VGN-FZ38M Battery) .

Fluorescent back-lights also contain mercury, whereas LED back-lights do not.

Materials recycling

Main articles: Electronic waste and computer recycling

Recycling computing equipment can keep harmful materials such as lead, mercury, and hexavalent chromium out of landfills, and can also replace equipment that otherwise would need to be manufactured, saving further energy and emissions (SONY VAIO VGN-FZ21m Battery) .

Computer systems that have outlived their particular function can be re-purposed, or donated to various charities and non-profit organizations. However, many charities have recently imposed minimum system requirements for donated equipment.Additionally, parts from outdated systems may be salvaged and recycled through certain retail outlets and municipal or private recycling centers. Computing supplies, such as printer cartridges, paper, and batteries may be recycled as well (SONY VAIO VGN-FZ18m Battery) .

A drawback to many of these schemes is that computers gathered through recycling drives are often shipped to developing countries where environmental standards are less strict than in North America and Europe. The Silicon Valley Toxics Coalition estimates that 80% of the post-consumer e-waste collected for recycling is shipped abroad to countries such as China and Pakistan (SONY VAIO VGN-FZ11m Battery) .

The recycling of old computers raises an important privacy issue. The old storage devices still hold private information, such as emails, passwords and credit card numbers, which can be recovered simply by someone using software that is available freely on the Internet. Deletion of a file does not actually remove the file from the hard drive (SONY VAIO VGN-FZ31z Battery) .

Before recycling a computer, users should remove the hard drive, or hard drives if there is more than one, and physically destroy it or store it somewhere safe. There are some authorized hardware recycling companies to whom the computer may be given for recycling, and they typically sign a non-disclosure agreement (Sony VGN-FW11S Battery) .

Telecommuting

Main article: Telecommuting

Teleconferencing and telepresence technologies are often implemented in green computing initiatives. The advantages are many; increased worker satisfaction, reduction of greenhouse gas emissions related to travel, and increased profit margins as a result of lower overhead costs for office space, heat, lighting, etc (Dell Studio 1555 Battery,Dell Latitude D610 Battery) .

The savings are significant; the average annual energy consumption for U.S. office buildings is over 23 kilowatt hours per square foot, with heat, air conditioning and lighting accounting for 70% of all energy consumed. Other related initiatives, such as hotelling, reduce the square footage per employee as workers reserve space only when they need it (Dell Vostro 1500 Battery) .

Many types of jobs, such as sales, consulting, and field service, integrate well with this technique.

Voice over IP (VoIP) reduces the telephony wiring infrastructure by sharing the existing Ethernet copper. VoIP and phone extension mobility also made hot desking more practical (Toshiba Satellite M60 battery) .

Computer monitor

A monitor or display (sometimes called a visual display unit) is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors use a cathodic ray tube about as deep as the screen size (Dell XPS M1210 Battery) .

Originally computer monitors were used for data processing and television receivers for entertainment; increasingly computers are being used both for data processing and entertainment. Displays exclusively for data use tend to have an aspect ratio of 4:3; those used also (or solely) for entertainment are usually 16:9 widescreen, Sometimes a compromise is used, e.g. 16:10 (Dell Studio XPS 1340 Battery) .

Screen size

Main articles: Viewable image size and Computer display standard

For any rectangular section on a round tube, the diagonal measurement is also the diameter of the tube

The area of displays with identical diagonal measurements can vary substantially (Dell Studio XPS 1640 Battery)

The size of an approximately rectangular display is usually given as the distance between two opposite screen corners, that is, the diagonal of the rectangle. One problem with this method is that it does not take into account the display aspect ratio, so that for example a 16:9 21 in (53 cm) widescreen display is far less high, and has less area, than a 21 in (53 cm) 4:3 screen. The 4:3 screen has dimensions of 16.8 × 12.6 in (43 × 32 cm) and area 211 sq in (1,360 cm2), while the widescreen is 18.3 × 10.3 in (46 × 26 cm), 188 sq in (1,210 cm2) (Dell Vostro 1710 Battery) .

For many purposes the height of the display is the main parameter; a 16:9 display needs a diagonal 22% larger than a 4:3 display for the same height.

This method of measurement is inherited from the method used for the first generation of CRT television, when picture tubes with circular faces were in common use. Being circular, only their diameter was needed to describe their size (ASUS EEE PC900 battery) .

Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangle was equivalent to the diameter of the tube's face. This method continued even when cathode ray tubes were manufactured as rounded rectangles; it had the advantage of being a single number specifying the size, and was not confusing when the aspect ratio was universally 4:3 (Dell RM791 battery) .

A problematic practice was the use of the size of a monitor's imaging element, rather than the size of its viewable image, when describing its size in publicity and advertising materials. On CRT displays a substantial portion of the CRT's screen is concealed behind the case's bezel or shroud in order to hide areas outside the monitor's "safe area" due to overscan. These practices were seen as deceptive, and widespread consumer objection and lawsuits eventually forced most manufacturers to instead measure viewable size (Sony VGP-BPS13 battery) .

Performance measurements

The performance of a monitor is measured by the following parameters:

Luminance is measured in candelas per square meter (cd/m2 also called a Nit).

Viewable image size is measured diagonally. For CRTs, the viewable size is typically 1 in (25 mm) smaller than the tube itself (sony vgp-bpl9 battery) .

Aspect ratios is the ratio of the horizontal length to the vertical length. 4:3 is the standard aspect ratio, for example, so that a screen with a width of 1024 pixels will have a height of 768 pixels. If a widescreen display has an aspect ratio of 16:9, a display that is 1024 pixels wide will have a height of 576 pixels (Sony VGP-BPL11 battery) .

Display resolution is the number of distinct pixels in each dimension that can be displayed. Maximum resolution is limited by dot pitch.

Dot pitch is the distance between subpixels of the same color in millimeters. In general, the smaller the dot pitch, the sharper the picture will appear (Sony VGP-BPL15 battery) .

Refresh rate is the number of times in a second that a display is illuminated. Maximum refresh rate is limited by response time.

Response time is the time a pixel in a monitor takes to go from active (black) to inactive (white) and back to active (black) again, measured in milliseconds. Lower numbers mean faster transitions and therefore fewer visible image artifacts.

Contrast ratio is the ratio of the luminosity of the brightest color (white) to that of the darkest color (black) that the monitor is capable of producing (Dell Inspiron E1505 battery ) .

Power consumption is measured in watts.

Viewing angle is the maximum angle at which images on the monitor can be viewed, without excessive degradation to the image. It is measured in degrees horizontally and vertically (Dell Latitude E6400 battery) .

Comparison

CRT

Pros:

High dynamic range (up to around 15,000:1), excellent color, wide gamut and low black level.

Can display natively in almost any resolution and refresh rate (HP Pavilion dv6000 Battery)

No input lag

Sub-millisecond response times

Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.

Usually much cheaper than LCD or Plasma screens.

Allows the use of light guns/pens (Hp Pavilion dv3-1000 battery)

Cons:

Large size and weight, especially for bigger screens (a 20-inch unit weighs about 50 lb (23 kg))

High power consumption

Generates a considerable amount of heat when running

Geometric distortion caused by variable beam travel distances (Dell Precision M70 Battery)

Can suffer screen burn-in

Produces noticeable flicker at low refresh rates

Normally only produced in 4:3 aspect ratio

Hazardous to repair/service

Effective vertical resolution limited to 1024 scan lines (Acer Aspire One battery) .

Color displays cannot be made in sizes smaller than 7 inches (5 inches for monochrome). Maximum size is 21 inches (for computer monitors; televisions run up to 40 inches).

LCD

Pros:

Very compact and light (Toshiba Satellite L305 Battery)

Low power consumption

No geometric distortion

Little or no flicker depending on backlight technology

Not affected by screen burn-in

No high voltage or other hazards present during repair/service (Toshiba Satellite Pro M15 Battery)

More reliable than CRTs

Can be made in almost any size or shape

No theoretical resolution limit

Cons:

Limited viewing angle, causing color, saturation, contrast and brightness to vary, even within the intended viewing angle, by variations in posture (Toshiba Satellite M65 battery) .

Bleeding and uneven backlighting in some monitors, causing brightness distortion, especially toward the edges.

Slow response times, which cause smearing and ghosting artifacts. Modern LCDs have response times of 8 ms or less.

Only one native resolution. Displaying resolutions either requires a video scaler, lowering perceptual quality, or display at 1:1 pixel mapping, in which images will be physically too large or won't fill the whole screen (Toshiba Satellite T4900 Battery) .

Fixed bit depth, many cheaper LCDs are only able to display 262,000 colors. 8-bit S-IPS panels can display 16 million colors and have significantly better black level, but are expensive and have slower response time

Input lag

Dead pixels may occur either during manufacturing or through use (Toshiba PA3399U-2BRS battery) .

In a constant on situation, thermalization may occur, which is when only part of the screen has overheated and therefore looks discolored compared to the rest of the screen.

Not all LCD displays are designed to allow easy replacement of the backlight

Cannot be used with light guns/pens (Toshiba Satellite A200 Battery)

Plasma

Main article: Plasma display

Pros:

High contrast ratios (10,000:1 or greater,) excellent color, wide gamut and low black level.

High speed response.

Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.

No geometric distortion (Toshiba Satellite 1200 Battery) .

Softer and less blocky-looking picture than LCDs

Highly scalable, with less weight gain per increase in size (from less than 30 in (760 mm) wide to the world's largest at 150 in (3,800 mm)).

Cons:

Large pixel pitch, meaning either low resolution or a large screen (Toshiba NB100 Battery) .

Color plasma displays cannot be made in sizes under 32 inches

Noticeable flicker when viewed at close range

Heavy weight

Glass screen can induce glare and reflections

High operating temperature and power consumption (Toshiba Satellite M300 Battery)

Only has one native resolution. Displaying other resolutions requires a video scaler, which degrades image quality at lower resolutions.

Fixed bit depth

Can suffer image burn-in. This was a severe problem on early plasma displays, but much less on newer ones

Cannot be used with light guns/pens (Dell INSPIRON 1525 battery)

Dead pixels are possible during manufacturing

Problems

Phosphor burn-in

Phosphor burn-in is localized aging of the phosphor layer of a CRT screen where it has displayed a static image for long periods of time. This results in a faint permanent image on the screen, even when turned off. In severe cases, it can even be possible to read some of the text, though this only occurs where the displayed text remained the same for years (SONY VAIO VGN-FZ280E Battery) .

Burn-in is most commonly seen in the following applications:

Point-of-service applications

Arcade games

Security monitors (SONY VAIO VGN-FZ410 Battery)

Screen savers were developed as a means to avoid burn-in, which was a widespread problem on IBM Personal Computer monochrome monitors in the 1980s. Monochrome displays are generally more vulnerable to burn-in because the phosphor is directly exposed to the electron beam while in color displays, the shadow mask provides some protection. Although still found on newer computers, screen savers are not necessary on LCD monitors (SONY VAIO VGN-FZ160 Battery) .

Phosphor burn-in can be "fixed" by running a CRT with the brightness at 100% for several hours, but this merely hides the damage by burning all the phosphor evenly. CRT rebuilders can repair monochrome displays by cutting the front of the picture tube off, scraping out the damaged phosphor, replacing it, and resealing the tube. Color displays cannot be repaired (SONY VAIO VGN-FZ38M Battery) .

Plasma burn-in

Burn-in re-emerged as an issue with early plasma displays, which are more vulnerable to this than CRTs. Screen savers with moving images may be used with these to minimize localized burn. Periodic change of the color scheme in use also helps (SONY VAIO VGN-FZ21m Battery) .

Glare

Glare is a problem caused by the relationship between lighting and screen or by using monitors in bright sunlight. Matte finish LCDs and flat screen CRTs are less prone to reflected glare than conventional curved CRTs or glossy LCDs, and aperture grille CRTs, which are curved on one axis only and are less prone to it than other CRTs curved on both axes (SONY VAIO VGN-FZ18m Battery) .

If the problem persists despite moving the monitor or adjusting lighting, a filter using a mesh of very fine black wires may be placed on the screen to reduce glare and improve contrast. These filters were popular in the late 1980s. They do also reduce light output.

A filter above will only work against reflective glare; direct glare (such as sunlight) will completely wash out most monitors' internal lighting, and can only be dealt with by use of a hood or transreflective LCD (SONY VAIO VGN-FZ11m Battery) .

Color misregistration

With exceptions of correctly aligned video projectors and stacked LEDs, most display technologies, especially LCD, have an inherent misregistration of the color channels, that is, the centers of the red, green, and blue dots do not line up perfectly. Sub-pixel rendering depends on this misalignment; technologies making use of this include the Apple II from 1976 , and more recently Microsoft (ClearType, 1998) and XFree86 (X Rendering Extension) (SONY VAIO VGN-FZ11z Battery) .

Incomplete spectrum

RGB displays produce most of the visible color spectrum, but not all. This can be a problem where good color matching to non-RGB images is needed. This issue is common to all monitor technologies with three color channels (SONY VAIO VGN-FZ11l Battery) .

Display interfaces

Computer terminals

Main article: Computer terminal

Early CRT-based VDUs (Visual Display Units) such as the DEC VT05 without graphics capabilities gained the label glass teletypes, because of the functional similarity to their electromechanical predecessors (SONY VAIO VGN-FZ31z Battery) .

Some historic computers had no screen display, using a teletype, modified electric typewriter, or printer instead.

Composite signal

Early home computers such as the Apple II and the Commodore 64 used a composite signal output to drive a TV or color composite monitor (a TV with no tuner). This resulted in degraded resolution due to compromises in the broadcast TV standards used. This method is still used with video game consoles. The Commodore monitor had S-Video input to improve resolution, but this was not common on televisions until the event of HDTV (Sony VGN-FW11S Battery) .

Digital displays

Early digital monitors are sometimes known as TTLs because the voltages on the red, green, and blue inputs are compatible with TTL logic chips. Later digital monitors support LVDS, or TMDS protocols (Sony VGP-BPS13B/B Battery) .

TTL monitors

IBM PC with green monochrome display.

Monitors used with the MDA, Hercules, CGA, and EGA graphics adapters used in early IBM PC's (Personal Computer) and clones were controlled via TTL logic. Such monitors can usually be identified by a male DB-9 connector used on the video cable (Toshiba Satellite P10 Battery) .

The disadvantage of TTL monitors was the limited number of colors available due to the low number of digital bits used for video signaling .

Modern monochrome monitors use the same 15-pin SVGA connector as standard color monitors. They are capable of displaying 32-bit grayscale at 1024x768 resolution, making them able to interface with modern computers (SONY VAIO VGN-FZ210CE Battery) .

TTL Monochrome monitors only made use of five out of the nine pins. One pin was used as a ground, and two pins were used for horizontal/vertical synchronization. The electron gun was controlled by two separate digital signals, a video bit, and an intensity bit to control the brightness of the drawn pixels. Only four shades were possible; black, dim, medium or bright (Hp pavilion dv6000 battery) .

CGA monitors used four digital signals to control the three electron guns used in color CRTs, in a signaling method known as RGBI, or Red Green and Blue, plus Intensity. Each of the three RGB colors can be switched on or off independently. The intensity bit increases the brightness of all guns that are switched on, or if no colors are switched on the intensity bit will switch on all guns at a very low brightness to produce a dark grey (Sony VGN-FW11S Battery_) .

A CGA monitor is only capable of rendering 16 colors. The CGA monitor was not exclusively used by PC based hardware. The Commodore 128 could also utilize CGA monitors. Many CGA monitors were capable of displaying composite video via a separate jack.

EGA monitors used six digital signals to control the three electron guns in a signaling method known as RrGgBb. Unlike CGA, each gun is allocated its own intensity bit. This allowed each of the three primary colors to have four different states (off, soft, medium, and bright) resulting in 64 colors (Dell Studio 1555 Battery) .

Although not supported in the original IBM specification, many vendors of clone graphics adapters have implemented backwards monitor compatibility and auto detection. For example, EGA cards produced by Paradise could operate as an MDA, or CGA adapter if a monochrome or CGA monitor was used in place of an EGA monitor. Many CGA cards were also capable of operating as MDA or Hercules card if a monochrome monitor was used (Dell Vostro 1720 Battery) .

Single color screens

Green and amber phosphors were used on most monochrome displays in the 1970s and 1980s. White was uncommon because it was more expensive to manufacture, although Apple used it on the Lisa and early Macintoshes (Dell Vostro 1500 Battery) .

Modern technology

Analog monitors

Most modern computer displays can show the various colors of the RGB color space by changing red, green, and blue analog video signals in continuously variable intensities. These are almost exclusively progressive scan. Although televisions used an interlaced picture, this was too flickery for computer use. In the late 1980s and early 1990s, some VGA-compatible video cards in PCs used interlacing to achieve higher resolution, but the event of SVGA quickly put an end to them (Dell Latitude D830 Battery) .

While many early plasma and liquid crystal displays have exclusively analog connections, all signals in such monitors pass through a completely digital section prior to display.

While many similar connectors (13W3, BNC, etc…) were used on other platforms, the IBM PC and compatible systems standardized on the VGA connector in 1987 (Dell Latitude D620 Battery) .

CRTs remained the standard for computer monitors through the 1990s. The first standalone LCD displays appeared in the early 2000s and over the next few years, they gradually displaced CRTs for most applications. First-generation LCD monitors were only produced in 4:3 aspect ratios, but current models are generally 16:9. The older 4:3 monitors have been largely relegated to point-of-service and some other applications where widescreen is not required (SONY VAIO VGN-FZ150E Battery) .

Digital and analog combination

The first popular external digital monitor connectors, such as DVI-I and the various breakout connectors based on it, included both analog signals compatible with VGA and digital signals compatible with new flat-screen displays in the same connector. Older 4:3 LCD monitors had only VGA inputs, but the newer 16:9 models have added DVI (Dell Studio 1735 Battery) .

Digital monitors

Monitors are being made which have only a digital video interface. Some digital display standards, such as HDMI and DisplayPort, also specify integrated audio and data connections. Many of these standards enforce DRM, a system intended to deter copying of entertainment content (Dell Inspiron 300M Battery) .

Configuration and usage

Multiple monitors

Main article: Multi-monitor

More than one monitor can be attached to the same device. Each display can operate in two basic configurations (Dell Studio 1737 battery) :

The simpler of the two is mirroring (sometimes cloning,) in which at least two displays are showing the same image. It is commonly used for presentations. Hardware with only one video output can be tricked into doing this with an external splitter device, commonly built into many video projectors as a pass through connection (Dell XPS M1530 battery) .

The more sophisticated of the two, extension allows each monitor to display a different image, so as to form a contiguous area of arbitrary shape. This requires software support and extra hardware, and may be locked out on "low end" products by crippleware.

Primitive software is incapable of recognizing multiple displays, so spanning must be used, in which case a very large virtual display is created, and then pieces are split into multiple video outputs for separate monitors (Dell XPS M2010 battery) .

Hardware with only one video output can be made to do this with an expensive external splitter device, this is most often used for very large composite displays made from many smaller monitors placed edge to edge (Dell Vostro 1000 battery) .

Multiple video sources

Multiple devices can be connected to the same monitor using a video switch. In the case of computers, this usually takes the form of a "Keyboard Video Mouse switch" (KVM) switch, which is designed to switch all of the user interface devices for a workstation between different computers at once (HP Pavilion dv9000 battery) .

Virtual displays

Main article: Virtual desktop

Screenshot of workspaces layed out by Compiz

Much software and video hardware supports the ability to create additional, virtual pieces of desktop, commonly known as workspaces. Spaces is Apple's implementation of virtual displays (Hp 520 battery) .

Additional features

Power saving

Most modern monitors will switch to a power-saving mode if no video-input signal is received. This allows modern operating systems to turn off a monitor after a specified period of inactivity. This also extends the monitor's service life (SONY VGP-BPS13 Battery) .

Some monitors will also switch themselves off after a time period on standby.

Most modern laptops provide a method of screen dimming after periods of inactivity or when the battery is in use. This extends battery life and reduces wear (SONY VAIO VGN-FZ Battery) .

Integrated accessories

Many monitors have other accessories (or connections for them) integrated. This places standard ports within easy reach and eliminates the need for another separate hub, camera, microphone, or set of speakers (Dell RM791 battery) .

Glossy screen

Main article: Glossy display

Some displays, especially newer LCD monitors, replace the traditional anti-glare matte finish with a glossy one. This increases saturation and sharpness but reflections from lights and windows are very visible (Toshiba Portege R200 Battery) .

Directional screen

Narrow viewing angle screens are used in some security conscious applications.

Autopolyscopic screen

Main article: Autostereoscopy

A directional screen which generates 3D images without headgear (Toshiba Satellite M60 battery) .

Touch screen

These monitors use touching of the screen as an input method. Items can be selected or moved with a finger, and finger gestures may be used to convey commands. The screen will need frequent cleaning due to image degradation from fingerprints.

Tablet screens (Dell Vostro 1400 Battery)

Main article: Graphics tablet/screen hybrid

A combination of a monitor with a graphics tablet. Such devices are typically unresponsive to touch without the use of one or more special tools' pressure. Newer models however are now able to detect touch from any pressure and often have the ability to detect tilt and rotation as well.

Touch and tablet screens are used on LCD displays as a substitute for the light pen, which can only work on CRTs (HP Pavilion DV7 Battery) .