Computer case, Motherboard and PC Power Supply

form factors

Types:

AT
ATX
microATX
Mini-ITX
Nano-ITX
Pico-ITX
Baby-AT
BTX
DTX
ETX
FlexATX
LPX
Mini-DTX
NLX
WTX


Comparisons

The ATX (for Advanced Technology Extended) form factor was created by Intel in 1995. It was the first big change in computer
case and motherboard design in many years. ATX overtook AT completely as the default form factor for new systems. ATX
addressed many of the AT form factor's annoyances that had frustrated system builders. Other standards for smaller boards
(including microATX, FlexATX and mini-ITX) usually keep the basic rear layout but reduce the size of the board and the number
of expansion slot positions. In 2003, Intel announced the new BTX standard, intended as a replacement for ATX. As of January
2007 the ATX form factor remains the industry standard for do-it-yourselfers; BTX has however made inroads into pre-made
systems, being adopted by computer makers like Dell, Gateway, and HP.

The official specifications were released by Intel in 1995, and have been revised numerous times since, the most recent being
version 2.2[1], released in 2004.

A full size ATX board is 305mm wide by 244mm deep (12" x 9.6" ). This allows many ATX form factor chassis to accept
microATX boards as well.



The ATX (for Advanced Technology Extended) form factor was created by Intel in 1995. It was the first big change in computer
case and motherboard design in many years. ATX overtook AT completely as the default form factor for new systems. ATX
addressed many of the AT form factor's annoyances that had frustrated system builders. Other standards for smaller boards
(including microATX, FlexATX and mini-ITX) usually keep the basic rear layout but reduce the size of the board and the number
of expansion slot positions. In 2003, Intel announced the new BTX standard, intended as a replacement for ATX. As of January
2007 the ATX form factor remains the industry standard for do-it-yourselfers; BTX has however made inroads into pre-made
systems, being adopted by computer makers like Dell, Gateway, and HP.

The official specifications were released by Intel in 1995, and have been revised numerous times since, the most recent being
version 2.2[1], released in 2004.

A full size ATX board is 305mm wide by 244mm deep (12" x 9.6" ). This allows many ATX form factor chassis to accept microATX
boards as well.

Contents [hide]
1 Power supply
1.1 Dell power supplies
2 Connectors
3 Variants
4 Computer Power Supply form factors
5 See also
6 External links



[edit] Power supply

ATX form motherboards became increasingly popular because of their advantages over older AT motherboards.AT-style
computer cases had a power button that was directly connected to the system computer power supply (PSU). The general
configuration was a double-pole latching mains voltage switch with the four pins connected to wires from a four-core cable. The
wires were either soldered to the power button (making it difficult to replace the power supply if it failed) or blade receptacles
were used.



Typical ATX power supply

Interior view of an ATX power supply.An ATX power supply does not directly connect to the system power button, allowing the
computer to be turned off via software. However, many ATX power supplies have a manual switch on the back to ensure the
computer is truly off and no power is being sent to the components. With this switch on, energy still flows to the components
even when the computer appears to be "off." This is known as soft-off or standby and can be used for remote wake up through
Wake-on-Ring or Wake-on-LAN, but is generally used to power on the computer through a front switch.

The power supply's connection to the motherboard was changed. Older AT power supplies had two similar connectors that could
be accidentally switched, usually causing short-circuits and irreversible damage to the motherboard. ATX used one large, keyed
connector instead, making a reversed connection very difficult. The new connector also provided a 3.3 volt source, removing the
need for motherboards to derive this voltage from one of the other power rails. Some motherboards, particularly late model AT
form factor offerings, supported both AT and ATX PSUs.

ATX was originally designed with the power supply drawing air into the case and exhausting it down onto the motherboard. The
plan was to deliver cool air directly to the CPU's and power regulation circuitry's location, which was usually at the top of the
motherboard in ATX designs. This was not particularly useful for a variety of reasons. Early ATX systems simply didn't have
processors or components with thermal output that required special cooling considerations. Later ATX systems with significantly
greater heat output would not be aided in cooling by a power supply delivering its often significantly heated exhaust into the
case. As a result, the ATX specification was changed to make PSU airflow optional.[2]

With the introduction of the Pentium 4, the standard 20-pin ATX power connector was deemed inadequate to supply increasing
electrical load requirements. The standard was revised with an extra 4-pin, 12-volt connector. This was later adopted by Athlon
XP and Athlon 64 systems. Various high-end systems may have other forms of supplemental power connections.

Because video card power demands have dramatically increased over the 2000s, some high-end graphics cards have power
demands that exceed AGP or PCIe slot capabilities. For these cards, supplementary power was delivered through a standard
power connector like those used for hard drives or floppy drives. PCI Express-based video cards manufactured after 2004
typically use a standard 6 or 8-pin PCIe power connector directly from the PSU.

Because the ATX PSU uses the motherboard's power switch, turning on the power in situations that do not utilize an ATX
motherboard is possible by shorting the green wire from the ATX connector to any black wire on the connector (or ground). This
allows re-use of an old PC power supply for tasks other than powering a PC, but one must be careful to observe the minimum
load requirements of the PSU.

The ATX form factor has had five main power supply designs throughout its lifetime:

ATX — 20 pin connector (Used through Pentium III and early Athlon XP)
WTX — 24 pin connector (Pentium II and III, Xeon and Athlon MP)
AMD GES — 24 pin main connector, 8 pin secondary connector (some dual-processor Athlon)
EPS12V — 24 pin main connector, 8 pin secondary connector, optional 4 pin tertiary connector (Xeon and Opteron) defined in
SSI specification
ATX12V — 20 pin main connector, 4 pin secondary connector, 8 pin tertiary connector (Pentium 4 and mid/late Athlon XP &
Athlon 64)
ATX12V 1.3 — guidance for the −5 volt feed was removed. This was only used by legacy ISA add-in cards
ATX12V 2.0 — 24 pin main connector, 4 pin secondary connector (Pentium 4, Core 2 Duo, and Athlon 64 with PCI Express)
ATX12V 2.2 — One 20/24-pin connector, one ATX12V 4 pin connector. Many power supply manufacturers include a 4 plus 4
pin, or 8 to 4 pin secondary connector instead, which can also be used as the secondary EPS12V connector.
24-pin ATX power supply connector
(20-pin omits the last 4: 11, 12, 23 and 24) Color Signal Pin Pin Signal Color
+3.3 V 1 13 +3.3 V sense  
+3.3 V 2 14 −12 V  
Ground 3 15 Ground  
+5 V 4 16 Power on  
Ground 5 17 Ground  
+5 V 6 18 Ground  
Ground 7 19 Ground  
Power good 8 20 −5 V (optional)  
+5 V standby 9 21 +5 V  
+12 V 10 22 +5 V  
+12 V 11 23 +5 V  
+3.3 V 12 24 Ground  


[edit] Dell power supplies

Older Dell computers, particularly those from the Pentium II and III times, are notable for using proprietary power wiring on their
power supplies and motherboards. While the motherboard connectors appear to be standard ATX, and will actually fit a standard
power supply, they are not compatible. Not only have wires been switched from one location to another, but the number of wires
for a given voltage has been changed. Thus, the pins cannot simply be rearranged.[3]

The change affects not only 20-pin ATX connectors, but also auxiliary 6-pin connectors. Modern Dell systems may use standard
ATX connectors.[4] Dell PC owners should be careful when attempting to mix non-Dell motherboards and power supplies, as it
can cause damage to the power supply or other components. If the power supply color coding on the wiring does not match ATX
standards, then it is probably proprietary. Wiring diagrams for Dell systems are usually available on Dell's support page.



[edit] Connectors

ATX I/O platesOn the back of the system, some major changes were made. The AT standard only had a keyboard connector
and expansion slots for add-on card backplates. Any other onboard interfaces (such as serial and parallel ports) had to be
connected via flying leads to connectors which were mounted either on spaces provided by the case or brackets placed in
unused expansion slot positions. ATX allowed each motherboard manufacturer to put these ports in a rectangular area on the
back of the system, with an arrangement they could define themselves (though a number of general patterns depending on what
ports the motherboard offers have been followed by most manufacturers). Generally the case comes with a snap out panel, also
known as an I/O plate, reflecting one of the common arrangements. If necessary, I/O plates can be replaced to suit the
arrangement on the motherboard that is being fitted and the I/O plates are usually included when purchasing a motherboard.
Panels were also made that allowed fitting an AT motherboard in an ATX case.

ATX also made the PS/2-style mini-DIN keyboard and mouse connectors ubiquitous. AT systems used a 5 pin DIN connector for
the keyboard, and were generally used with serial port mice (although PS/2 mouse ports were also found on some systems).
Many modern motherboards are phasing out the PS/2-style keyboard and mouse connectors in favor of the modern standard of
USB ports. Other legacy connectors that appeared on ATX motherboards but are being phased out include 25-pin parallel ports
and 9-pin serial ports. In their place, on-board Ethernet and audio ports are increasingly common.


[edit] Variants

This short section requires expansion.

There exist several ATX-derived form factors that use the same power supply, mountings and basic back panel arrangement but
set different standards for the size of the board.


ATX Scale Reference  width length color in image
FlexATX 9 inches (228.6 mm) 7.5 inches (190.5 mm)  
microATX 9.6 inches (243.8 mm) 9.6 inches (243.8 mm)  
EmbATX (embedded ATX) 9.6 inches (243.8 mm) 9.6 inches (243.8 mm)  
Mini ATX 11.2 inches (284.5 mm) 8.2 inches (208.3 mm) (none)
Standard ATX 12 inches (304.8 mm) 9.6 inches (243.8 mm)  
EATX (extended ATX) 12 inches (304.8 mm) 13 inches (330.2 mm)  
WTX (workstation ATX) 14 inches (355.6 mm) 16.75 inches (425.4 mm)  
picoBTX (203.20 mm) (266.70 mm) (none)
nanoBTX (223.52 mm) (266.70 mm) (none)
microBTX (264.16 mm) (266.70 mm) (none)
BTX (325.12 mm) (266.70 mm) (none)


[edit] Computer Power Supply form factors

ATX
WTX
TFX
SFX
CFX
LFX


[edit] See also

mini-ITX
BTX
SSI CEB



ATX Computer power supplies

The power supply converts the alternating current (AC) line from your home to the direct current (DC) needed by the personal
computer.In a personal computer (PC), the power supply is the metal box usually found in a corner of the case. The power
supply is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan. Typical
computer power supply generates the voltages needed by the computer motherboard accessories. A typical modern PC power
supply generates the following voltages:

+5V (+-5%) at up to tens of amperes for motherboard electronics, disk drives and cards
+12V (+-10%) at several ampreres for disk drives and some cards
+3.3V (+-5%) up to tens of amperes for the majority of modern logic electronics in motherboard
-12V (+-10%) usully less than one ampere for some accessory cards
Most other computer power supplies usually give voltage on this line, because those are the most commonly used voltage used
in computer systems. Depending on the PC model, power supplies are rated anywhere between 150 and 350 W. A PC power
supply on average is rated for 250-400 watts. PSUs above300W are unusual and only tend to come in servers, or machines
thathave been designed for 'hardcore' applications such as gaming, where ahundred watt graphics card is not that unusual.
Typically if you have 300W available, and the computer is going to be usingperhaps 150-220 W of that, depending on what's in
it. Pc power are designed to provide +12, +5, -5 and -12 (usualy nowadays also +3.3V), with the power spread unevenly across
those ranges. Grab an averagecomputer PSU and take a look at it, and there will probably be a tableon it listing how many amps
can be delivered per voltage category.PC power supplies are mainly primary switching power supplies with power switches
arranged in a half-bridge configuration. The outputs can drive the usual 20 A (+5 V), 8 A (+12 V) and 0,5 A (-12 V, -5 V) at
approx. 205 W output power. (modern ATX power supplies add considerable amount of 3.3V to this).A typical efficiency of a PC
power supply is around 75 %. A typical power PC supply measures around 140 x 100 x 50 mm (W, D, H) and weights around
300-400 grams. The switching frequency of approx. 33 kHz is usual for PC power supplies. The PC power supplies can be
generally found at AT and ATX varieties. The older PCs used to use AT power supplies. Those power supplies supplied +5V,
+12V, -12V, and -5V power to motherboard. Practically all new PCs use ATX format power supplies which have added to the
picture following extra functions: +3.3V output, program/pushbutton turn on, standaby power (low current +5V output to some
parts inside PC when the main power supply is off) and option to turn power supply off with software control.
Laptop computers use slightly different approach for power supply. Modern laptop computer typically comes with a switched
mode poer supply that plugs to the wall and supplies the needed power to the computer at some suitable low voltage. A typical
voltage that those mains adapters supply to laptop are in 16-24V range, the actual voltage used can vary between different
computer brands and models (check the computer manual and/or power supply markings for more details). The power supplied
by this kind of power supply is typically in aroun d 40-60W range maximum (check your computer manual and/or power supply
for information on your system). The internal power supply electronics inside the laptop then generate the multiple voltages
needed inside the laptop (typically at least 5V, 3.3V and processor internal core voltage). If you need to power your laptop from
car voltage (12V), you have two options to do this: use a DC to AC converter or a DC-DC converter. When you use DC to AC
inverter, you first take the car power (typically 12V from lighter plug) and turn it to a normal mains voltage (110-120V AC or 220-
240V AC depending where you live) power. Then the normal PC wall power supply is used to convert this power to voltage used
by the laptop. This approach could work, but has it's downsides. The downsides are poor efficiency (power lost, both converter
and laptop PSU get hot), and potential incompatibility with the DC to AC converter and computer power supplies. The DC to AC
converters genrally do not like computer power supply type load (very non-linear load that takes high current splikes, can lead to
unreliable operation and potential converter failure) and the computer power supply might not always like the non-sinusoidal
mains power that is put out by most cheap DC to AC converters (can cause more heating on power supply, even power supply
damages). An expensive high power sinewave DC to AC converter should work well with any load, also with computer power
supplies, but is expensive. Another usually better approach is to use a DC-DC converter that replaces the original computer
mains power supply. It takes in car 12V power and output the same output voltage that the normal mains adapter gives out. This
kind of adapters are available from several laptop manufacturers. An adapter from the same manufacturer as your laptop is
usually the easiest and safest choise, nut not usually cheapest option. Nowadays there are also quite cheap general purpose
laptop DC-DC converters that can be adapted to be used with many different laptops. Those adapters have typically an
adjustable output voltage (should be adjusted to match you specific computer). Just select an adapter that can be adjusted to
your laptop operating and has high enough power rating (same or higher power rating as the original mains adapter), and things
should work well. Please note that in some cases using a DC-DC converter not approved by the computer manufacturer can
void your laptop warranty.


General information

ATX Power/Cooling - ATX power supply is different from AT power supply. It depends a logic circuit on the motherboard to turn it
on.
ATX
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