1. Motherboard Form Factors The form factor determines the general layout, size, and feature
placement on a motherboard. Different form factors usually require different style cases. Differences
between form factors can include; physical size and shape, mounting hole location, feature placement,
power supply connectors, and others. Form Factor Specifications
12" 11-13" Very Old PCs Full AT, Full Tower
8.5" 10-13" Older PCs All but Slimline, ATX
12" 9.6" Newer PCs ATX
11.2" 8.2" Newer PCs ATX
9.6" 9.6" Specialty PCs Slimline
9.0" 7.5" Specialty PCs Custom Design
9" 11-13" Older Retail PCs Slimline
8-9" 10-11" Older Retail PCs Slimline
8-9" 10-13.6" Newer Retail PCs Slimline
AT Form Factor The AT form factor is the oldest and the biggest form factor. It was popular until the
Baby AT was released, which was around the time of the 386 processor (1992-93). The reason that
prompted the Baby AT was the width of the AT (12") and the fact that the board was difficult to install,
service, and upgrade. BABY AT The Baby AT was the standard in the PC industry from roughly 1993-
1997. It is still being used today, usually in Pentium class products.
Some issues with the AT and Baby AT design is the location of the features on the board. The CPU
socket is placed so that it may interfere with longer bus cards. In some designs the memory sockets are
similarly placed. This can limit the amount and selection of peripheral cards you can install. Also the IO
ports are separate and mounted on the case and connected to pin-outs on the motherboard. These are
usually located near the floppy and IDE pin-outs and can result in quite a jumble of ribbon cables.
ATX ATX was developed as an evolution of the Baby AT form factor and was defined to address four
areas of improvement: enhanced ease of use, better support for current and future I/O, better support for
current and future processor technology, and reduced total system cost.
The ATX is basically a Baby AT rotated 90 degrees and providing a new mounting configuration for the
power supply. The processor is relocated away from the expansion slots, allowing them to hold full length
add-in cards. The longer side of the board is used to host more on-board I/O. The ATX power supply,
rather than blowing air out of the chassis, as in most Baby AT platforms, provides air-flow through the
chassis and across the processor.

2. Mini-ATX
This form factor is basically the same as ATX with a smaller allowable board size.
ATX = 12" x 9.6"
Mini-ATX = 11.2" x 8.2"
microATX
This form factor was developed as a natural evolution of the ATX form factor to address new market
trends and PC technologies. microATX supports:
Current processor technologies
The transition to newer processor technologies
AGP high performance graphics solutions
Smaller motherboard size
Smaller power supply form factor
FlexATX
A subset of the microATX design. FlexATX offers the opportunity for system developers to create many
new personal computer designs. FlexATX allows enhanced flexibility where conforming motherboards
may be enclosed; that is, all-in-one computing devices, LCD-personal computers, or standard desktop
systems.
This form factor is designed to allow very custom case and board designs to be manufactured. For
example; The NBA could commission computers that looked like basketballs. There is not too much limit
on the shape of the board and case. We should see some very interesting system designs emerging
from this form factor.
Supports current socketed processor technologies
Smaller motherboard size

3. ATX 2.03 I/O panel
Same mounting holes as microATX
Socket only processors to keep the size small
LPX & Mini LPX
This is based on a design by Western Digital. The expansion slots are on a single riser card which is
mounted onto the planar board. Mainly OEM manufacturers (i.e. Packard Bell/NEC, Dell, etc) use these
boards.
LPX is an older form factor (8.67" x 9.25") that has been replaced by NLX. The LPX form factor is usually
found in desktop model PCs. The LPX case is a slim-line, low-profile case with a riser card arrangement
for expansion cards. This means that expansion boards are parallel to the motherboard, rather than
perpendicular to it as in other common form factors, such as AT and ATX. This allows for smaller cases,
but limits the number of expansion slots, usually to two or three.
LPX motherboards often have the video adapters integrated onto the motherboard, and they may have
integrated sound as well. This can provide a high-quality product at low cost, but can make upgrading or
repair difficult. It is not always possible to disable the built-in video adapter cards to allow for an upgrade.
LPX motherboards also usually come with serial, parallel, and mouse connectors attached to them, like
ATX.
The LPX case and motherboard design are not designed for a home PC builder, as they can be cramped
and difficult to work in, as well as being non-standard. They also offer poor expandability, poor
upgradability, poor cooling, and difficulty of use for the home PC builder.
NLX
NLX is a new low profile motherboard form factor designed to improve upon today’s low profile form
factors and to adapt to new market trends and PC technologies. NLX does the following:
Supports current and future processor technologies
Supports new Accelerated Graphics Port (A.G.P.) high performance graphics solutions
Supports tall memory technology
Provides more system level design and integration flexibility; for example, the new design
flexibility allows system designers to implement a motherboard that can be removed quickly, in
most cases without removing screws, thus lowering the PC’s total cost of ownership.
The picture above shows an example of an NLX board and riser.

4. The add-in card riser is located at the right edge of the motherboard (as viewed from the front).
The processor is located at the front, left section of the motherboard, improving thermal and
clearance issues.
Taller components such as the processor and tall memory are preferred to be located on the left
side of the motherboard, allowing the I/O slots to hold full length add-in cards in many system
configurations.
At the back of the motherboard (as viewed from the front), the I/O connectors are stacked single
and double high to support more connectors.
Several major PC vendors world-wide worked jointly to define the NLX form factor and to incorporate
flexibility to accommodate the best designs for current and future PCs. NLX is a public specification
intended for widespread use in many types of systems.
Also see Motherboard FAQ.