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I/O Connector Port Holes or I/O Template(s)
Your PC would not be of much use unless you could interact with it, and to do that you
need to be able to connect to the main PC box your I/O peripherals, such as your keyboard,
mouse, printer and so on. The cables from these devices actually connect to the
motherboard, and therefore holes are provided in the case to permit access to the ports
that attach to the motherboard (either by direct mounting, or via internal cables from
ports mounted to the case). There are two different ways that this is done, depending
primarily on the form factor (and thus the age) of the system.
On older XT, AT, Baby AT and LPX cases, there are a number of discrete holes in the
case itself, in the shapes necessary to accomodate the round keyboard connector, and
"D-shaped" serial and parallel connectors. On XT, AT and Baby AT systems, ports
were installed to these holes, with the connector facing out from the hole, and cables
running from the inside of the port to the motherboard. Since some systems included more
parallel ports than others, since some serial ports were 9-pin and others 25-pin, and
since it was desirable to leave room for expansion, many of these older cases included
more holes in the case than some motherboards required. Therefore, to keep out dirt and
ensure proper air circulation in the case, most manufacturers covered unused I/O port
holes. Some cases had discrete port covers that screwed in place, while other case makers
just manufactured the back panel of the case with sheet metal punchouts where the ports
would go, and the installer would remove the appropriate ones. On LPX systems the holes
were placed to line up with one of the standard configurations of I/O ports installed
directly to the LPX motherboard, instead of mounting ports to the case itself.
Closeup of I/O port holes (one keyboard, two 9-pin
and two 25-pin serial/parallel) on the back of a typical
Baby AT form factor tower case. Note that the sheet metal
"punchouts" are still in place in the serial and parallel port holes.
The black keyboard connector on the motherboard is visible
through the case's keyboard hole.
Original image © Kamco Services
Image used with permission.
Newer form factors, including ATX (and its variants), NLX, and WTX, specify that the
I/O ports be mounted directly onto the motherboard in either a single or double row. A
wide variety of configurations is possible, to provide motherboard manufacturers the
flexibility to design solutions for various PC requirements. To accomodate this
flexibility, cases designed for these form factors did away with the rigidly-placed I/O
port holes in favor of interchangeable plates with different configurations and patterns
of holes. These removable metal plates are called I/O templates, or sometimes, I/O
shields. Often, a case will come with templates that correspond to one or more of the
most popular motherboard designs used with that case, but these may not match up well with
every motherboard. You may need to get a suitable replacement template from your
A set of ATX I/O templates showing hole patterns
different motherboard I/O port configurations. From left, a single-row
I/O port template; a double-row template; and a template with
just a keyboard connector hole. The last template could be used to
allow installation of an AT form factor motherboard in a combo
AT/ATX case. Serial and parallel port holes would of course need
to be elsewhere on the back of the case for the AT motherboard.
Image © PC Power & Cooling, Inc.
Image used with permission.
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