Do You Know And What Understanding I/O Devices

Do You Know And What Understanding I/O Devices

The Input/Output (I/O) unit is the part of the microprocessor system that the microprocessor uses to communicate with the outside world.

The input unit is an external unit that is used to enter data from outside into this microprocessor, for example data from a keyboard or mouse. While the output unit is usually used to display data, or in other words to capture data sent by the microprocessor, for example data to be displayed on a monitor or printer screen.

The input (input) and also the output (output) parts also require control signals, among others, to read I/O (Input/Output Read [IOR]) and to write I/O (Input/Output Write [IOW]).

I/O port which means the input/output connector gate on a computer, such as a keyboard, parallel/serial mouse or USB. Provides connections for external devices such as digital cameras, printers and scanners.

Here is some Example I/O Device Below:

1. Keyboard

A keyboard (English: keyboard) or keyboard is a device for typing or entering certain letters, numbers, or symbols into the software or operating system run by the computer.

The keyboard consists of rectangular keys with letters, numbers, or symbols printed on them. In some operating systems, when two keys are pressed at the same time, a special function or a preset shortcut is created.

There are different types of layout of buttons on the keyboard. However, the most popular and commonly used is the QWERTY layout, mimicking the typewriter layout system.

New types of keyboards usually have additional keys above the function keys (F1, F2, etc.) to make it easier for users to operate the computer. In addition, many new keyboards also support wireless technology.

2. Mouse

A mouse is a device used to enter data into a computer other than a keyboard. The mouse got its name because the wires that stick out are shaped like a mouse’s tail.

The mouse was first made in 1963 by Douglas Engelbart made of wood with one button. The second model is equipped with 3 buttons. In 1970, Douglas Engelbart introduced a mouse that can determine the XY position on a computer screen, this mouse is known as the XY Position Indicator (XY position indicator).

The most common form of mouse has two buttons, one on the top left and one on the top right that can be pressed. However, Macintosh-based computers typically use a one-button mouse.

The mouse works by capturing movement using a ball that hits a hard, flat surface. More modern mice don’t use balls anymore but use optical beams to detect motion. In addition, some are already using wireless technology, whether based on radio, infrared light, or Bluetooth.

Currently, the latest technology has made it possible for mice to use a laser system so that the resolution can reach 2,000 dots per inch (dpi), some can even reach 4,800 dots per inch. Usually this model mouse is for video game fans.

3. Printer

A printer or printer is a device that displays data in printed form, either in the form of text or images/graphics, on paper. Printers are usually divided into several parts, namely a picker as a tool to take paper from the tray. Tray is a place to put paper. Ink or toner is a real printer, because there is something called ink or toner that is used to write on paper. The difference between toner and ink is a system difference; toner or laser need heating, while ink or inkjet does not need heating, only cleaning or cleaning the print-head of the printer.

There is also a flexible cable for sending signals from the printer processor to the ink or toner. These cables are thin and flexible, yet powerful. On the back of the printer there is usually a parallel or USB port for connecting to a computer.

The modem printer is a powerful tool. The electronic equipment contained in a printer is the same as the electronic equipment contained in the computer itself. The printer has 6 types, namely Dot-Matrix type, Daisy Wheel type, Ink-Jet type / Bubble Jet type, Chain type, Drum type and Laser type.

4. scanner

A scanner or scanner is a tool used to scan a shape or property of objects, such as documents, photos, waves, temperature and others. The scan results will generally be transformed into a computer as digital data. There are several types of scanners depending on how they are used and how they work, including:

1. image scanner
2. barcode scanner
3. X-ray scanner
4. check scanner
5. metal scanner
6. Optical Mark Reader (OMR) scanner

Among these types of scanners, image scanners are the most commonly referred to as scanners. Like the OMR scanner, the image scanner can also be used as a Computer Answer Sheet (LJK) scanner. In order to achieve this, software with Digital Mark Reader (DMR) technology is needed.

When grouped by way of loading paper, there are 2 types of image scanners, namely:

1. flatbed
In Flatbed image scanners, the paper is placed on top of the scanner glass, then a light and scanner sensor will move along the paper to obtain the image.

2. Automatic Document Feeder (ADF)
In the Automatic Document Feeder (ADF) image scanner, the paper is placed in the tray/tray, and then one by one the paper will be loaded by the mechanical part of the scanner with a pad assy and roller. When the paper moves over the scanner lamp, the scanner sensor works to obtain an image that represents the paper. The advantages of the Automatic Document Feeder (ADF) scanner are:

1. high speed, can reach > 10,000 sheets per hour
2. can read two sides of the paper at the same time
3. with the imprinter, the scanner can mark the sheets that have been scanned
4. Perfectly paired with software with Digital Mark Reader technology and for – archiving and document management

Definition of Storage

Computer data storage, derived from English “computer data storage” is often referred to as computer memory, referring to computer components, computer equipment, and recording media that retain digital data that is used for some time interval.

Computer data storage provides one of the three core functions of modern computers, namely retaining information. It is one of the fundamental components found in all modern computers, and is closely related to the microprocessor, and has been the computer model used since the 1940s.

In contemporary usage, computer memory refers to a form of semiconductor storage media, known as Random Access Memory (RAM), and sometimes other forms that are faster but can only store data temporarily.

However, the term “computer storage” now generally refers to mass storage media, which can be optical disks, some forms of magnetic storage media (such as hard disks) and other types of storage media that are slower than RAM, but have properties more permanent, like flash memory.

1. Memory

Memory is a generic term for data storage in a computer. Some types of memory that are widely used are as follows:

1. Processor registers
2. RAM or Random Access Memory
3. Cache Memory (SRAM) (Static RAM)
4. Physical memory (DRAM) (Dynamic RAM)
5. Magnetic disk-based storage device
6. Optical disk-based storage device
7. Read-only memory or ROM (Read Only Memory)
8. Flash Memory
9. Punched Card (ancient)
10. CD or Compact Disk
11. DVD

In talking about computer architectures such as the von Neumann architecture, for example, memory capacity and speed are distinguished by using a memory hierarchy. This hierarchy is arranged from the fastest to the slowest memory types; arranged from the smallest capacity to the largest capacity; and sorted from the price of each bit of memory starting from the highest (expensive) to the lowest (cheap).

Processor registers:

Processor register in computer architecture is a small amount of computer memory that works at very high speed which is used to execute computer programs by providing fast access to commonly used values. Generally, the values ​​that are commonly used are the values ​​that are being executed at a certain time.

The processor register stands at the highest level in the memory hierarchy: this means that its speed is the fastest; the capacity is the smallest; and the price of each bit is the highest. Registers are also used as the fastest way in computer systems to manipulate data. Registers are generally measured by units of bits that can be accommodated by them, such as “8-bit registers”, “16-bit registers”, “32-bit registers”, or “64-bit registers” and others.

The term register currently can refer to a collection of registers that can be indexed directly to input/output an instruction defined by the instruction set. For this term, the word “Architectural Registry” is used. For example, the Intel x86 instruction set defines a set of eight 32-bit registers, but a CPU implementing the x86 instruction set can contain more than eight 32-bit registers.

Register type

1. Registers are divided into several classes:
2. Data register, which is used to store numbers in integers (integers).
3. Address register, which is used to store memory addresses and also to access memory.
4. General purpose register, which can be used to store numbers and addresses simultaneously.
5. Floating-point register, which is used to store floating-point numbers.
6. Constant registers (constant registers), which are used to store fixed numbers that can only be read (read-only), such as phi, null, true, false and others.
7. Vector register, which is used to store the results of vector processing performed by the SIMD processor.
8. Special purpose registers that can be used to store processor internal data, such as instruction pointers, stack pointers, and status registers.

Machine-specific registers (machine-specific registers), in some architectures, are used to store data or settings related to the processor itself. Because the meaning of each register is directly incorporated into the design of a particular processor, it is possible that registers of this type may not become standard between generations of processors.

Register size


What is RAM and Full form of RAM(Random access memory)

Random access memory (English: Random access memory, RAM) is a type of computer storage whose contents can be accessed at any time regardless of where the data is in memory. This is in contrast to sequential memory devices, such as magnetic tapes, disks and drums, where the mechanical movement of the storage medium forces the computer to access data sequentially.

First known in the 60’s. It’s just that at that time semiconductor memory was not yet popular because the price was very expensive. It was more common to use magnetic main memory. Semiconductor companies such as Intel debuted by producing RAM, more precisely the type of DRAM.

Usually, RAM can be written to and read, as opposed to read-only-memory (ROM), RAM is usually used for primary storage (main memory) in a computer for active use and conversion of information, although some devices use several types. RAM to provide long-term secondary storage.

But there are also those who argue that ROM is another type of RAM, because it is actually Random Access like SRAM or DRAM. It’s just that the writing process on ROM requires a special process that is not as easy and flexible as SRAM or DRAM. In addition, some part of the RAM address space (main memory) of a system is mapped onto one or two ROM chips.

Common types of RAM

1. SRAM or Static RAM
2. NV-RAM or Non-Volatile RAM
3. DRAM or Dynamic RAM
– Fast Page Mode DRAM
– EDO RAM or Extended Data Out DRAM
– SDRAM or Synchronous DRAM
– DDR SDRAM or Double Data Rate Synchronous DRAM is now (2005) starting to be replaced with DDR2
4. RDRAM or Rambus DRAM

What is Uncommon type of RAM

Dual-ported RAM
Video RAM, dual-port memory with one random access port and one sequence access port. He became popular as more and more people needed video memory. See the explanation in Dynamic RAM.

3. FeRAM

Top-ranking manufacturer of RAM

1. Infineon
2. Hynix
3. Samsung
4. Micron
5. Rambus
6. Corsair

What is ROM and Full Form of ROM(Read-only Memory) and types of ROM

Read-only Memory (ROM) is an English term for a data storage medium on a computer. ROM stands for Read-Only Memory, this ROM is one of the existing memory in the computer. This ROM is permanent, meaning that the program/data stored in this ROM is not easily lost or changed even though the electricity is turned off.

Storing data on ROM can not be done easily, but reading data from ROM can be done easily. Usually, the program/data contained in this ROM is filled by the factory that made it. Because of this property, ROM is commonly used to store firmware (software that is closely related to hardware).

One example of ROM is the BIOS ROM which contains the basic computer system program that manages/prepares all equipment/components that exist in the computer when the computer is turned on. Modern ROM is found in IC form, just like other storage/memory mediums such as RAM. To distinguish it, you need to read the text listed on the IC. Usually starts with the number 27xxx, the number 27 indicates the type of ROM, xxx indicates the capacity in kilobits (not kilobytes).

Mask ROM

The data on the ROM is entered directly through the mask at the time of chip assembly. This makes it very economical especially if we produce in large quantities. But it also becomes very expensive because it is not flexible. A change of even one bit requires a new mask which is of course not cheap. Because it is not flexible, it is rare for anyone to use it anymore.

Another application that is similar to ROM is the prerecorded CD-ROM that we are familiar with, one of which is music CDs. Contrary to the opinion of many people that CD-ROMs are written with a laser, in fact the data on a CD-ROM is more precisely printed on a plastic disk.

ROM types

1. Mask ROM
6. Flash Memory

Flash memory

Flash memory is a type of EEPROM that allows multiple memory locations to be erased or written to in a single programming operation. In layman’s terms, it is a form of writable memory chip, unlike random access memory/RAM chips, this memory can store its data without requiring a power supply. This memory is commonly used in memory cards, USB flash drives, MP3 players, digital cameras, and mobile phones.


CD-ROM (short for Compact Disc – Read Only Memory) is a compact disc of the optical disc type that can store data. The size of data that can be stored today can reach 700MB or 700 million bytes.

CD-ROM is read only (can only be read, and can not be written). To be able to read the contents of a CD-ROM, the main tool needed is a CD Drive. The development of the latest CD-ROM allows CDs to be written repeatedly (Re-Write / RW) which is better known as CD-RW.


Compact Disk Rewritable, abbreviated as CD-RW, is a rewritable CD-ROM. A CD-RW uses the same size media as a CD-R. but instead of using cyanine or pthalocyanine dyes, CD-RW uses a metal alloy of silver, indium, antimony, and tellurium for the recording layer.

CD-RW drives use lasers of three different powers. At high power, the laser melts the alloy metal, converting it from a high reflectivity crystalline state to an amorphous reflectivity state to resemble a pit. At moderate power, the alloy melts and changes back in its natural crystalline state to become land again. At low power, the state of the material is checked (for readings), but no phase transition occurs.

CD-RW discs are relatively more expensive than CD-R discs


DVD is a kind of optical disc that can be used to store data, including movies with better video and audio quality than VCD quality. “DVD” was originally an abbreviation of digital video disc, but some parties want the abbreviation to be changed to digital versatile disc to make it clear that this format is not just for video.

Since a consensus between these two parties could not be reached, now the official name is simply “DVD”, and the letters “officially” don’t stand for anything. There is also software that allows users to back up their own DVDs such as DVD Decrypter and DVD Shrink.

What is Motherboards

The motherboard is the central printed circuit board (PCB) in some complex electronic systems, such as modern personal computers. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple computers, logic board. It is also sometimes commonly abbreviated as mobo.


Prior to the advent of the microprocessor, computers were usually built in card-case enclosures or mainframes with components connected by a backplane consisting of a series of slots themselves connected by cables; in very old designs it was discrete wiring connections between card connector pins, but printed circuit boards soon became standard practice. The central processing unit, memory and peripherals are located on individual printed circuits that plug into the backplane.

In the late 1980s and 1990s, it became economical to move more and more peripheral functions to the motherboard (see below). In the late 1980s, motherboards began to include a single IC (called Super I/O chips) capable of supporting a set of low-speed peripherals: keyboard, mouse, floppy disk drive, serial port, and parallel port. Until the late 1990s, most personal computer motherboards supported complete audio, video, storage, and network functionality without the need for any expansion cards at all; Higher-end systems for 3D gaming and computer graphics usually only retained the graphics card as a separate component.

The early pioneers of motherboard manufacturing were Micronics, Mylex, AMI, DTK, Hauppauge, Orchid Technology, Elitegroup, DFI, and a number of Taiwan-based manufacturers.

Popular personal computers such as the Apple II and IBM PC have published schematic diagrams and other documentation that permitted rapid reverse-engineering and replacement of third-party motherboards. Usually intended to build new computers compatible with the examples, many of the motherboards offer additional performance or other features and are used to upgrade the original factory equipment.

The term mainboard is archaically applied to a device with a single board and no additional or expansion capabilities. In modern terms this would include embedded systems, and controlling boards in televisions, washing machines etc. Motherboards specifically refer to Printed Circuits with the ability to increase/expand performance/capabilities with the addition of “daughterboards”.

Most computer motherboards manufactured today are designed for IBM-compatible computers, which currently account for about 90% of global PC sales. A motherboard, like the backplane, provides the electrical connections through which other components of the system communicate, but unlike the backplane, it also hosts the central processing unit, and other subsystems and devices.

Motherboards are also used in many other electronic devices such as cell phones, stop-watches, clocks, and other small electronic devices. A typical desktop computer has a microprocessor, main memory, and other important components on the motherboard. Other components such as external storage, controllers for display video and sound, and peripherals may need to be attached to the motherboard as plug-in cards or via cables, although modern computers are increasingly common to integrate some of these peripherals onto the motherboard itself.

An important component of the motherboard is the supporting microprocessor chipset, which provides a supporting interface between the CPU and the various bus and external components. This chipset determines, to a certain extent, the features and capabilities of this motherboard.

Modern motherboards include, at a minimum:

a socket (or slot) in which one or more microprocessors are installed slots into a system whose main memory is installed (usually in the form of DIMMs containing DRAM chip modules) a chipset that forms an interface between the CPU’s front-side bus, main memory, and a device bus non-volatile memory chips (usually Flash ROM in modern motherboards) containing the system firmware or BIOS a clock generator that generates system clock signals to synchronize the various components of the slot for the expansion card (this interfaces to the system via buses supported by the chipset) power connector flashes, which receive electrical power from the computer’s power supply and distribute it to the CPU, chipset, main memory, and expansion cards.

CPU socket

A CPU socket or CPU slot is an electrical component that is attached to a printed circuit board (PCB) and designed to house the CPU (also called a microprocessor). This is a special type of integrated circuit socket designed for very high pin count. A CPU socket provides a variety of functions, including providing a physical structure to support the CPU, providing support for the heat sink, facilitating replacement (as well as reducing costs) and most importantly establishing an electrical interface with both the CPU and PCB. The CPU socket can most often be found on most desktop and server computers (laptops usually use a surface mount CPU), especially those based on the Intel x86 architecture on the motherboard.

Integrated peripherals

With the continued decline in the cost and size of integrated circuits, it is now possible to include support for multiple peripherals on the motherboard. By combining multiple functions on a single PCB, the physical size and total cost of the system can be reduced; Highly-integrated motherboards are thus very popular in small form factor and budget computers.

For example, the ECS RS485M-M,[6] which is typical of modern budget motherboards for AMD processor-based computers, has enormous on-board support for a variety of devices:

1. disk controller for floppy disk drives, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0 / 1 support)
2. Integrated ATI Radeon graphics controller supports 2D and 3D graphics, with VGA and TV output
3. The integrated sound card supports 8-channel (7.1) audio and S/PDIF output
4. Fast Ethernet network controller for 10/100 Mbit networking
5. USB 2.0 controller supporting up to 12 USB ports
6. IrDA controller for infrared data communication (e.g. with an IrDA enabled Cellular Phone or Printer)
7. software temperature, voltage, and fan speed sensors that allow for monitoring the health of computer components

An expansion card to support all of these functions would have cost hundreds of dollars even a decade ago, but as of April 2007 such high-end integrated motherboards are available for as little as $30 in the US.

Peripheral card slot

Typical 2009 motherboards will have a different number of connections depending on the standard. Standard ATX motherboards usually have 1x PCI-E 16x connections for graphics cards, 2x PCI slots for various expansion cards and 1x PCI-E 1x which will eventually replace PCI.

Super standard ATX motherboards will have 1x PCI-E 16x connections for graphics cards. It will also have a different number of PCI and PCI-E 1x slots. Sometimes it can also have a PCI-E 4x slot. This varies between brands and models.

Some motherboards have 2x PCI-E 16x slots, to allow for more than 2 monitors without special hardware or to allow the use of special graphics technologies called SLI (for nVidia) and CrossFire (for ATI). This allows 2 graphics cards to be linked together, to enable better performance in computationally intensive graphics tasks, such as gaming and video-editing.

As of 2007 almost all motherboards come with at least 4x USB ports on the back, with a minimum of 2 connections on the internal board for wiring additional front ports built into the computer case. Ethernet is also included now. This is a standard network cable for connecting a computer to a network or modem. A sound chip is always included on the motherboard, to allow for sound output without the need for additional components. This allows computers to be much more multimedia-based than ever before. Now cheap machines often have a graphics chip built into the motherboard instead of a separate card.

Temperature and reliability

Motherboards are generally air-cooled with heat sinks often mounted on a larger chip, such as the northbridge, of modern motherboards. If the motherboard is not cooled properly, it can cause the computer to crash. Passive cooling, or a single fan attached to the power supply, was sufficient for many desktop computer CPUs until the late 1990s; since then, most require CPU fans mounted on heat sinks, due to increased clock speed and power consumption.

Most motherboards have connectors for additional case fans as well. Newer motherboards have integrated temperature sensors to detect the temperature of the motherboard and CPU, and a controlled fan connector which the BIOS or operating system can use to regulate fan speed. Some high-powered computers (which typically have high-performance processors and large amounts of RAM, as well as high-performance video cards) use a water cooling system instead of multiple fans.

Some small form factor computers and home theater PCs are designed for quiet and energy-efficient fan-less designs. This usually requires the use of a low-power CPU, as well as a careful layout of the motherboard and other components to allow for the placement of the heat sink.

A 2003 study found that some fake computer crashes and general reliability issues, ranging from screen image distortion to I/O read/write errors, can’t be attributed to software or hardware, but to aging capacitors on PC motherboards. Finally, this is shown as a result of faulty electrolyte formulation.

Motherboards use electrolytic capacitors to filter the DC power distributed around the board. These capacitors age at a temperature-dependent rate, as the water-based electrolyte evaporates slowly. This can lead to loss of capacitance and subsequent malfunction of the motherboard due to voltage instability.

While most capacitors are rated for 2000 hours of operation at 105°C, the design expects their life to double for every 10°C below this. At 45°C a lifetime of 15 years can be expected. This seems reasonable for computer motherboards, but many manufacturers have delivered substandard capacitors, which significantly reduces life expectancy. Cases of inadequate cooling and high temperatures easily exacerbate this problem.

It is possible but tedious and time consuming, to locate and replace failed capacitors on PC motherboards; it is cheaper to buy a new motherboard than to pay for repairs.

form factor

Motherboards are manufactured in a variety of sizes and shapes, some of which are specific to each computer manufacturer. However, the motherboards used in IBM-compatible commodity computers have been standardized to suit various case sizes. As of 2007 most desktop computer motherboards use one of these standard form factors—even those found in Macintosh and Sun computers that haven’t been traditionally built from commodity components.

Laptop computers generally use highly integrated, miniature, and customized motherboards. This is one of the reasons that laptops are difficult to upgrade and expensive to repair. Often the failure of one component of a laptop requires the replacement of the entire motherboard, which is usually more expensive than desktop motherboards due to the large number of components integrated.

Nvidia SLI and ATI Crossfire

Nvidia SLI and ATI CrossFire technologies allow two or more of the same series of graphics cards to be linked together to enable faster graphics processing capabilities. Almost all mid to high-end nVidia cards and most high-end ATI cards support the technology.

They both require compatible motherboards. There is a clear need for 2x PCI-E 16x slots to allow two cards to be inserted into the computer. The same functionality can be achieved in the 650i motherboard by NVIDIA, with a pair of x8 slots. Initially, the tri-Crossfire was achieved at 8x speed with two 16x slots and one 8x slot; albeit at a slower pace. ATI opened the technology up to Intel in 2006, and all-new Intel chipsets now support Crossfire.

SLI is a bit more exclusive in requirements. It requires a motherboard with Nvidia’s own nForce series chipset to allow it to run (exception: select Intel X58 chipset-based motherboard).

It’s important to note that SLI and Crossfire typically won’t scale to 2x the performance of a single card when using a dual setup. They also do not double the effective amount of memory or VRAM bandwidth.

Bootstrapping using BIOS

The motherboard contains some non-volatile memory to initialize the system and load an operating system from some external peripheral devices. Microcomputers such as the Apple II and IBM PC used ROM chips, mounted in sockets on the motherboard. At power-up, the load center processor will program its counter with the boot ROM address, and start executing the ROM instructions, displaying system information on the screen and running memory checks, which in turn will start loading memory from an external device or device (disk drive). If it is not available, then the computer may perform tasks from other memory stores or display error messages, depending on the model and design of the computer and the BIOS version.

Most modern motherboard designs use a BIOS, stored in an EEPROM chip that is soldered to the motherboard, to bootstrap the motherboard. (Socketed BIOS chips are used extensively, too.) By booting on the motherboard, memory, circuitry, and devices are tested and configured. This process is known as a computer Power-On Self Test (POST) and may include testing some of the following devices:

1. floppy drive
2. network controller
3. CD-ROM drive
4. DVD-ROM drive
5. SCSI hard drives
6. IDE, EIDE, or SATA hard drives
7. External USB memory storage device

Each of the above devices can be stored with machine code instructions to load an operating system or program.


The PSU is the component that supplies power to other components in the computer. More specifically, power supply units are typically designed to convert a general-purpose alternating current (AC) from the mains (100-127V in North America, parts of South America, Japan, and Taiwan; 220-240V in most of the rest of the world) for low use. DC power voltage for the internal components of the computer. Some power supplies have a switch to switch between 230 V and 115 V. Other models have sensors that automatically switch input voltages, or can accept voltages between these limits.

Most common computer power supplies are built to conform to the ATX form factor. This allows different power supplies to be interchanged with different components in the computer. ATX power supplies are also designed to turn on and off using signals from the motherboard and provide support for modern functions such as the standby mode available on many computers. The latest standard specification for ATX PSU as of mid-2008 is version 2.31.

Note that some manufacturers, notably Compaq and Dell, have produced power supplies using the same connectors as ATX but with different voltages on various pins; such a mismatch of PSUs and motherboards can result in damage to one or both of them.

Power rating

Computer power supplies are rated based on maximum output power. Typical power ranges from 300 W to 500 W (lower than 300 W for Small form factor systems) and is intended for typical home computers, limited use to internet-surfing and burning and playing DVDs. The power supplies used by most gamers and enthusiasts range from 450 W to 1400 W.

Typical gaming PC features feature power supplies in the 500-800 W range, with higher PC demands 800-1400 W supplies. The highest-end units are up to 2 kW powerful and are intended primarily for servers and, to a lesser extent, extreme performance computers with multiple processors, multiple hard disks and multiple graphics cards (ATI CrossFire or NVIDIA SLI). The power rating of a PC power supply is not officially certified and claimed by the respective manufacturers.

A common way of achieving power figures for PC PSUs is to increase the available power on each rail, which will not give a true power figure. Therefore it is possible to overload a PSU on one rail without having to use the maximum rated power.

Sometimes ranking manufacturers inflate their power, in order to gain an advantage in the market. This can be done in the absence of clear standards for marking of power supplies and testing. Some of the main methods used are…

1. Advertising peak power, not perpetual power;
2. Determining the continuous power output capability is unrealistic at low temperatures (at room temperature as opposed to 40°C, which is more likely the temperature inside the PC case);
3. Total power advertises as a measure of capacity, when modern systems rely almost entirely on the available current of the 12-volt line(s).

This may mean that if:

1. PSU A has a peak rating of 550 watts at 25°C, with 25 amps (300 W) on the 12-volt line, and
2. PSU B has a continuous rating of 450 watts at 40°C, with 33 amps (400 W) on the 12-volt line, and those ratings are accurate, so PSU B should be considered a very superior unit, despite its overall lower rating. power ratings. A PSU may only be capable of delivering a portion of its rated power under real-world conditions. This trend has led in turn to highly overspecified power supply recommendations, and a shortage of high-quality power supplies with reasonable capacities. Very few computers require more than a maximum of 300-350 watts. [2] Higher-end computers such as server computers and game machines with multiple high-power GPUs are among the few exceptions.


Most computer power supplies are a square metal box, and have a large bundle of wires protruding from one end. Opposite to the tie wire is the electrical return face, with air vents and an IEC C14 connector for supplying AC power. There can optionally be a power switch and/or a voltage selector switch.

A label on one side of the box lists technical information about the power supply, including safety certifications maximum output power. Common certification marks for safety are the UL mark, GS mark, TÜV, NEMKO, SEMKO, DEMKO, FIMKO, CCC, CSA, VDE, GOST R and BSMI. Common certificate marks for EMI/RFI are the CE, FCC and C-tick marks. The CE mark is required for power supplies sold in Europe and India.

A RoHS or 80 PLUS can also sometimes be seen.

The dimensions of an ATX power supply are 150 mm wide, 86 mm high, and typically 140 mm deep, although depth may vary from brand to brand.

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