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ATX and Mini ATX
ATX represents the modern era
of motherboards. The ATX dethroned the AT and Baby AT form
factors and is found commonly in most computers today. The ATX originally
housed the Intel Pentium Pro and Pentium II processors and of course
has moved on to the current Pentium IV.
Lets start with a summary of
the ATX form factor. It measures 12 inches (30,48 cm) wide and 9.6 inches
(24,38 cm) deep while the smaller scale version called the Mini ATX
measures 11.2 inches (28,45 cm) wide by 8.2 inches (20,83 cm) deep.
The major improvement of the ATX over prior designs was not just one
of size and shape but it specified completely different case and power
supply requirements. Since this is the modern form factor,
the ATX will be recognizable by all technicians who commonly work on
personal computers. Even without opening up the case, you will see
the familiar PS/2 mouse connector and the keyboard connector as well
as four USB connectors. Of course there will also be a serial connector
and a parallel (printer) connector as well as a monitor connector and
an on board audio card. The ATX also has built in soft
power support instead of the toggle style power switch used by the AT
ATX85 was introduced in 1995 by Intel however; it did
not really start catching on until the Pentium Pro. Contrary to statements
on the web (and possibly the correct choice, if not a technically correct
answer on the A+ test), not all Pentium Pro motherboards were ATX.
Here are the specific differences
between an AT and ATX boards:
- Integrated I/O Connectors: ATX boards
have the actual ports built right onto the board. This makes installation
easier and improves reliability.
An integrated PS/2 mouse connection and the keyboard connection were
also reduced in size from the 5 pin DIN to a PS/2. Later on, these
became color coded with blue for the keyboard and green for the mouse.
If you happen to be the roughly 10% of males86 who have the most common type of visual color blindness
<deuteranopic87> (red/green) burn green mouse into
your brain. This factoid may come in handy later.
- Reduced Overlap between Board and Drives:
The ATX board is rotated 90 degrees so that it does and makes it easier
to work on the system board without working around or uninstalling a
drive as well as reducing heat.
- Reduced Processor Interference with Cards:
As the CPU has increased heat output (a 1/8 square CPU can now
equal the heat generated of a 100-Watt light bulb) heat sinks have gotten
larger. Therefore, Intel has moved the CPU from the front of the board
near the slots to the back and top of the board, near the power supply.
This made installing a full-length card less of an issue.
- User-Friendly Power Connector: ATX uses
one 20-pin (2 by 10) keyed connector to attach to the motherboard.
This is easier than the two connectors that look almost the same in
the AT design. No longer do you have to remember to adjoin P8 and P9
connectors so the black cables are next to each other when installing
- Better Cooling Conditions: Placing the
CPU closer to the power supply provides for better cooling.
- 3.3 Volt Power: The ATX motherboard is
designed to accept 3.3-Volt power directly from the power supply. Since
almost all modern processors operate at 3.3 Volts, this removes the
need for a voltage regulator on the motherboard to reduce the voltage
from 5V to 3.3V.
- Soft Switch: The AT power supply uses
a mechanical switch to supply power (or not). In the ATX, the power
is always on. It may be in standby mode (making the computer appear
'off'). The beauty of a 'soft switch' as found in the ATX is, this
makes it possible to return the system to a full power state, sometimes
called Wake on with Wake On Modem88, Wake on Keyboard/Mouse89 or WOL (Wake On LAN) with a magic packet90. This last feature is really a money saver. You
can broadcast to an entire group of computers on a LAN and push an application
update out during off hours.
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