Motherboard Form Factor

Motherboard

The motherboard is the main circuit board inside the PC.

It holds the CPU and memory, provides expansion slots

for peripherals, and, whether directly or indirectly,

connects to every part of the PC.

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

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.

BABY AT

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.

ATX

ATX

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.

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

microATX

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.

FlexATX

FlexATX

Supports current socketed processor technologies

Smaller motherboard size

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.

LPX

LPX & Mini LPX

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.

LPX & Mini LPX

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.

NLX

The picture shows an example of an NLX board and riser.

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.

NLX