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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 rugged construction.
The 7561 is a derivative of the PS/2 model 70: It also has Microchannel slots, a PS/S hard disk interface and the same power supply, but one slot more and a completely different housing with a large (and noisy...) fan at the front. The fan has a dust filter for use in 'dirty' environments.
I currently cannot make much use of my 7561 because it's broken somewhere in the area of the on-board VGA; I suspect the Color Palette DAC but it seems to be difficult to fix...
It almost looks like the designers of the 7561 took the innards of a model 70 and built a new metal case around it. The construction is exactly like the model 70, 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.
So you could have a built-in UPS for this machine - very nice in an industrial environment...