PC Form Factors

AT Form Factor
- Invented by IBM in the early 1980s
- Predominant form factor for motherboards up to the mid-1990s
- Now an obsolete form factor
- Had various size variations ranging from large to very large (ex. Baby AT motherboard)
- All AT motherboards have split power socket called P8/P9
- Contains a dedicated AT keyboard port
- AT motherboards lacked external/expansion ports (because when computer were first made there weren't many expansion cards or other computer hardware devices which plugged into computers)
- AT form factor variations: LPX form factor and NLX form factor

ATX Form Factor
- Created in 1995, overtook the AT form factor as most common form factor in 1998
- Most common form factor today
- Does NOT contain dedicated AT keyboard port
- Contains mini-DIN (PS/2) keyboard and mouse ports
- RAM placed closer to the Northbridge and CPU than on AT motherboards making ATX motherboards perform better
- Use soft power, meaning they can use software to turn a computer on and off
- ATX form factor subtypes: microATX and FlexATX

microATX Form Factor (subtype of ATX Form Factor)
- 9.6 by 9.6 inches in size
- 30% smaller than the ATX form factor
- microATX motherboards can fit into both a standard ATX case or a smaller microATX computer case

FlexATX Form Factor (subtype of ATX Form Factor)
- Created in 1999 by Intel
- Variant of the microATX form factor
- FlexATX motherboards have a maximum size of 9 by 7.5 inches making them the smallest motherboards of the ATX form factors
- most FlexATX systems use a special FlexATX-only power supply, although they can also use a standard ATX power supply

BTX Form Factor
- Balanced Technology eXtended form factor
- Three subtypes: standard BTX, microBTX and picoBTX
- BTX motherboards can't be placed in an ATX case and vice versa
- BTX uses the same power connection as the ATX form factor.  There is no such thing as a BTX power supply, it is just a marketing gimmick
- BTX designed to improve cooling in computers.  Pull cool air in from front of computer case and vent hot air out the back of case.
- CPU is moved/positioned to the front area of the computer case so cooler air flows past it
- Defines a special heat sink and fan assembly called the "thermal unit" which blows the hot CPU air directly out the back of case

Proprietary Form Factors
- Created by computer companies like Dell and Sony which make motherboards work/fit only in their specific cases