Content by Alfred Arnold (original HERE).
Edited by Major Tom.
The IBM 7561 belongs to a side-development of IBM's Personal Computer
Division that builds PCs for industrial use. In such environments, it is
not so important how cool a computer looks, but instead how good it can
withstand the environmental conditions. This leads to a solid full-metal
case that fits into 19-inch racks, extra cooling fans and a generally more
The 7561 is a derivative of the Japanese
PS/55 Model 5550-T. It uses
the same planar with four Micro Channel slots, a
DBA-ESDI hard disk interface and the same
power supply. However it has a completely different housing with a large (and
noisy...) fan at the front. The fan has a dust filter for use in 'dirty'
It almost looks like the designers of the 7561 took the innards of a PS/55
Model 5550 and built a new metal case around it. The internal construction is
exactly like the aforementioned machine, including the snap-in mountings for
hard drive and floppies.
Note the seemingly unused space left to the planar. Louis' first thought
was that it is the place of the optional battery pack, but it turned out
that the battery pack is located in supply: that:
The 7561 had a 180W PSU, autoranging option.
I was wrong then, but I put out the correct answer- the backup battery
fits inside the PSU itself. The screw that opens up it's compartment is
at the front of the PSU on the outside. The plug is a three pin Molex.
So you could have a built-in UPS for this machine - very nice in an