|You've probably heard the term motherboard a thousand times, but do you know what it really means and how it relates to the rest of your computer?
factor of a motherboard determines the specifications for its general shape and size. It also specifies what type
of case and power supply will be supported, the placement of
mounting holes, and the physical layout and organization of the
board. Form factor is especially important if you
build your own computer systems and need to ensure that you purchase the correct
case and components.
The Succession of Motherboard Form
AT & Baby AT
Prior to 1997, IBM computers used large motherboards.
After that, however, the size of the motherboard was reduced and boards using
the AT (Advanced Technology) form
factor was released. The AT form factor is found in older computers
(386 class or
earlier). Some of the problems with this form factor mainly arose from the
physical size of the board, which is 12" wide, often causing the
board to overlap with space required for the
Following the AT form factor, the
Baby AT form factor was introduced. With the Baby AT form factor the
width of the motherboard was decreased from 12" to 8.5", limiting
problems associated with overlapping on the drive bays' turf. Baby AT became popular
and was designed for peripheral devices such as the
and video to be contained on
circuit boards that were connected by
way of expansion slots on the motherboard.
Baby AT was not without problems
however. Computer memory itself advanced, and the Baby AT form
factor had memory sockets at the front of the motherboard.
As processors became
larger, the Baby AT form factor did not allow for space to use a
heatsink, and fan.
The ATX form factor was then designed
to overcome these issues.
Key Terms To
Understanding Motherboard Form Factors
The main circuit board of a microcomputer.
The physical size and shape of a device. It is often used to
describe the size of circuit boards.
Short for advanced technology, the AT is an IBM PC model introduced
The modern-day shape and layout of PC motherboards.
The BTX specification provides new tools and design space for
developers to lay out desktop systems, whether designing small,
compact systems or very large, expandable systems.
The form factor used by most PC motherboards prior to 1998.
With the need for a more
integrated form factor which defined standard
locations for the keyboard, mouse,
I/O, and video connectors, in the mid
1990's the ATX form factor was introduced. The ATX form factor brought about
many chances in the computer. Since the expansion slots were put onto
separate riser cards that plugged into the motherboard, the overall size of
the computer and its case was reduced. The ATX form factor specified changes
to the motherboard, along with the case and power supply. Some of the design
specification improvements of the ATX form factor included a single 20-pin
connector for the power supply, a power supply to blow air into the case
instead of out for better air flow, less overlap between the
motherboard and drive bays, and integrated I/O Port connectors soldered directly
onto the motherboard. The ATX form factor was an overall better design for upgrading.
MicroATX followed the ATX form factor and offered the same benefits but
improved the overall system design costs through a reduction in the physical
size of the motherboard. This was done by reducing the number of I/O slots
supported on the board. The microATX form factor also provided more I/O
space at the rear and reduced emissions from using integrated I/O
White ATX is the most well-known and used form factor, there is also a
non-standard proprietary form factor which falls under the name of LPX, and
LPX form factor is found in low-profile cases (desktop model as opposed to a
tower or mini-tower) with a riser card arrangement
for expansion cards where expansion boards run parallel to the motherboard.
While this allows for smaller cases it also limits the number of
expansion slots available. Most LPX motherboards have sound and video
integrated onto the motherboard. While this can make for a low-cost and
product they are generally difficult to repair due to a lack of space and
overall non-standardization. The LPX form factor is not suited to upgrading
and offer poor cooling.
Boards based on the NLX form factor hit the market in the late 1990's. This
"updated LPX" form factor offered support for larger memory modules, tower
cases, AGP video support and reduced cable length. In addition, motherboards
are easier to remove. The NLX form factor, unlike LPX is an actual standard which means there
is more component options for upgrading and repair.
Many systems that were formerly designed to
fit the LPX form factor are moving over to NLX. The NLX form factor is
well-suited to mass-market retail PCs.
The BTX, or Balanced
Technology Extended form factor, unlike its predecessors
is not an evolution of a previous form factor but a total break
away from the popular and dominating ATX form factor.
BTX was developed to take
advantage of technologies such as
USB 2.0, and
Changes to the layout with the BTX form factor include better component
placement for back panel I/O controllers and it is smaller than microATX
systems. The BTX form factor provides the
industry push to
tower size systems with an increased number of system slots.
One of the most talked
about features of the BTX form factor is that it uses
in-line airflow. In the BTX form factor the
memory slots and expansion slots have switched places, allowing the main
chipset, and graphics controller) to use the same airflow which reduces the
number of fans needed in the system; thereby reducing noise. To assist in
noise reduction BTX system level acoustics have been improved by a reduced
air turbulence within the in-line airflow
Initially there will
be three motherboards offered in BTX form factor. The first, picoBTX
will offer four mounting holes and one expansion slot, while microBTX
will hold seven mounting holes and four expansion slots, and lastly,
regularBTX will offer 10 mounting holes and seven expansion slots.
The new BTX form factor design is
incompatible with ATX, with the exception of being able to use an ATX power
supply with BTX boards.
Today the industry accepts the ATX form
factor as the standard, however
legacy AT systems are still widely in use. Since
the BTX form factor design is
incompatible with ATX, only time will tell if it will overtake ATX as the
Did You Know...
ATX and Baby AT boards are approximately the same size, but the
ATX board is rotated 90 degrees within the case to allow for
easier access to components.
Vangie 'Aurora' Beal
Last updated: April 29, 2005
ATX Form Factor
This PDF file contains the v2.1 ATX Form Factor specification.
Form Factor (PDF)
micro-ATX Motherboard Interface Specification v.1.2
BTX Form Factor (PDF)
This PDF file contains the
v1.0a BTX Form Factor
NLX Form Factor
This PDF file contains the
v1.8 NLX Form Factor