Computer Form Factor
Overview of form factors
Overview of form factors
A PC motherboard is the main circuit board within a typical desktop computer, laptop or server. Its main functions are as follows:
to serve as a central backbone to which all other modular parts such as CPU, RAM, and hard drives can be attached as required to create a modern computer;
to accept (on many motherboards) different components (in particular CPU and expansion cards) for the purposes of customization;
to distribute power to PC components;
to electronically co-ordinate and interface the operation of the components.
As new generations of components have been developed, the standards of motherboards have changed too; for example, with AGP being introduced, and more recently PCI Express. However, the standardized size and layout of motherboard have changed much more slowly, and are controlled by their own standards. The list of components a motherboard must include changes far more slowly than the components themselves. For example, north bridge controllers have changed many times since their introduction, with many manufacturers bringing out their own versions, but in terms of form factor standards, the requirement to allow for a north bridge has remained fairly static for many years.
Although it is a slower process, form factors do evolve regularly in response to changing demands. The original PC standard (AT) was superseded in 1995 by the current industry standard ATX, which still dictates the size and design of the motherboard in most modern PCs. The latest update to the ATX standard was released in 2004. A divergent standard by chipset manufacturer VIA called EPIA (also known as ITX, and not to be confused with EPIC) is based upon smaller form factors and its own standards.
Differences between form factors are most apparent in terms of their intended market sector, and involve variations in size, design compromises and typical features. Most modern computers have very similar requirements, so form factor differences tend to be based upon subsets and supersets of these. For example, a desktop computer may require more sockets for maximal flexibility and many optional connectors and other features on-board, whereas a computer to be used in a multimedia system may need to be optimized for heat and size, with additional plug-in cards being less common. The smallest motherboards may sacrifice CPU flexibility in favor of a fixed manufacturer's choice.
Comparisons
Tabular information
Form factor
Originated
Max. size
Typical feature-set
(compared to ATX)
Typical CPU
flexibility
Power handling
Notes
(typical usage, Market adoption, etc)
XT
IBM 1983
8.511in
216279mm
Obsolete, see Industry Standard Architecture. The IBM Personal Computer XT was the successor to the original IBM PC, its first home computer. As the specifications were open, many clone motherboards were produced and it became a de facto standard.
AT (Advanced Technology)
IBM 1984
121113in
305279330mm
Obsolete, see Industry Standard Architecture. Created by IBM for the IBM Personal Computer/AT, an Intel 80286 machine. Also known as Full AT, it was popular during the era of the Intel 80386 microprocessor. Superseded by ATX.
Baby-AT
IBM 1985
8.51013in
216254330mm
IBM's 1985 successor to the AT motherboard. Functionally equivalent to the AT, it became popular due to its significantly smaller size.
ATX
Intel 1996
129.6in
305244mm
Created by Intel in 1995. As of 2007[update], it is the most popular form factor for commodity motherboards. Typical size is 9.612in although some companies extend that to 1012in.
SSI CEB
SSI
1210.5in
305267mm
Created by the Server System Infrastructure (SSI) forum. Derived from the EEB and ATX specifications. This means that SSI CEB motherboards have the same mounting holes and the same IO connector area as ATX motherboards.
microATX
1996
9.69.6in
244244mm
A smaller variant of the ATX form factor (about 25% shorter). Compatible with most ATX cases, but has fewer slots than ATX, for a smaller power supply unit. Very popular for desktop and small form factor computers as of 2007[update].
Mini-ATX
AOpen 2005
5.95.9in
150150mm
Mini-ATX is slightly smaller than Mini-ITX. Mini-ATX motherboards were design with MoDT (Mobile on Desktop Technology) which adapt mobile CPU for lower power requirement, less heat generation and better application capability.
FlexATX
Intel 1999
9.07.5in
228.6190.5mm max.
A subset of microATX developed by Intel in 1999. Allows more flexible motherboard design, component positioning and shape. Can be smaller than regular microATX.
Mini-ITX
VIA 2001
6.76.7in
170170mm max.
A small, highly-integrated form factor, designed for small devices such as thin clients and set-top boxes.
Nano-ITX
VIA 2003
4.74.7in
120120mm
Targeted at smart digital entertainment devices such as PVRs, set-top boxes, media centers and Car PCs, and thin devices.
Pico-ITX
VIA 2007
10072mm max.
Mobile-ITX
VIA 2007
2.9531.772in
7545mm
BTX (Balanced Technology Extended)
Intel 2004
12.810.5in
325267mm max.
A standard proposed by Intel as a successor to ATX in the early 2000s, according to Intel the layout has better cooling. BTX Boards are flipped in comparison to ATX Boards, so a BTX or MicroBTX Board needs a BTX case, while an ATX style board fits in an ATX case.
MicroBTX (or uBTX)
Intel 2004
10.410.5in
264267mm max.
PicoBTX
Intel 2004
8.010.5in
203267mm max.
DTX
AMD 2007
200244mm max.
Mini-DTX
AMD 2007
200170mm max.
smartModule
Digital-Logic
6685mm
Used in embedded systems and single board computers. Requires a baseboard.
ETX
Kontron
95114mm
Used in embedded systems and single board computers. Requires a baseboard.
nanoETXexpress
Kontron
5584mm
Used in embedded systems and single board computers. Requires a carrier board. Also known as Nano COM Express Type 1
Extended ATX (EATX)
Unknown
1213in
305330mm
Used in rackmount server systems. Typically used for server-class type motherboards with dual processors and too much circuitry for a standard ATX motherboard. The mounting hole pattern for the upper portion of the board matches ATX.
LPX
Unknown
91113in
229279330mm
Based on a design by Western Digital, it allowed smaller cases than the AT standard, by putting the expansion card slots on a Riser card. Used in slimline retail PCs. LPX was never standardized and generally only used by large OEMs.
Mini-LPX
Unknown
891011in
203229254279mm
Used in slimline retail PCs.
PC/104
PC/104 Consortium 1992
3.83.6in
Used in embedded systems
AT Bus architecture adapted to vibration-tolerant header connectors.
PC104plus
PC/104 Consortium 1997
3.83.6in
Used in embedded systems.
PCI Bus architecture adapted to vibration-tolerant header connectors.
PCI/104Express
PC/104 Consortium 2008
3.83.6in
Used in embedded systems
PCI Express architecture adapted to vibration-tolerant header connectors.
NLX
Intel 1999
891013.6in
203229254345mm
A low-profile design released in 1997. It also incorporated a riser for expansion cards, and never became popular.
UTX
TQ-Components 2001
88108mm
Used in embedded systems and IPCs. Requires a baseboard.
WTX
Intel 1998
1416.75in
355.6425.4mm
A large design for servers and high-end workstations featuring multiple CPUs and hard drives.
XTX
2005
95114mm
Used in embedded systems. Requires a baseboard.
Please help improve this article by expanding it. Further information might be found on the talk page. (November 2007)
Graphical comparison of physical sizes
Maximum number of PCI/AGP/PCI-e slots
ATX case compatible:
Spec.
Number
ATX
7
MicroATX
4
FlexATX
3
Mini-DTX/DTX
2
Mini-ITX
1
Visual examples of different form factors
Different form factors
ATX
(Abit KT7)
mini-ITX
(VIA EPIA 5000AG)
Pico-ITX
(VIA EPIA PX10000G)
PC/104 and EBX
PC/104 is an embedded computer standard which defines both a form factor and computer bus. PC/104 is intended for embedded computing environments. Single board computers built to this form factor are often sold by COTS vendors, which benefits users who want a customized rugged system, without months of design and paper work.
The PC/104 form factor was standardized by the PC/104 Consortium in 1992. An IEEE standard corresponding to PC/104 was drafted as IEEE P996.1, but never ratified.
The 5.758.0in Embedded Board eXpandable (EBX) specification, which was derived from Ampro's proprietary Little Board form-factor, resulted from a collaboration between Ampro and Motorola Computer Group.
As compared with PC/104 modules, these larger (but still reasonably embeddable) SBCs tend to have everything of a full PC on them, including application oriented interfaces like audio, analog, or digital I/O in many cases. Also it's much easier to fit Pentium CPUs, whereas it's a tight squeeze (or expensive) to do so on a PC/104 SBC. Typically, EBX SBCs contain: the CPU; upgradeable RAM subassemblies (e.g., DIMM); Flash memory for solid state disk; multiple USB, serial, and parallel ports; onboard expansion via a PC/104 module stack; off-board expansion via ISA and/or PCI buses (from the PC/104 connectors); networking interface (typically Ethernet); and video (typically CRT, LCD, and TV).
Mini PC
Mini PC is a PC form factor very close in size to an external CD or DVD drive.
Examples
AOpen XC mini
Apple's Mac mini
References
^ http://www.windowsfordevices.com/c/a/News/Atom-module-shrinks-to-nano-size Atom module shrinks to nano size
^ image
The official Intel Form factors website containing form factor descriptions
See also
Small form factor
Hard-disk-drive form factors
Categories: Computer hardwareHidden categories: Articles lacking sources from July 2008 | All articles lacking sources | Articles containing potentially dated statements from 2007 | All articles containing potentially dated statements | Articles to be expanded from November 2007 | All articles to be expanded
Computer Form Factor
By: mumu
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