My Computer Collection
IBM PS/2 Model 85

Photo of IBM PS/2 Model 85
Click here or click onto the photo for a full size version of this picture.

The Model 85 was designed by IBM as a successor for the Model 80. In contrast to the Model 80, it was purely designed to be a server; the 76 and 77 had already taken the position as desktop workstations. In many respects, the Model 85 was more modern and better adapted to 'mainstream peripherals' than its predecessor. The case is wider and less tall allowing to install 5,25-inch drives horizontally. Instead of the two full-height bays that were difficult to use for half-height drives, there are five half-height bays, with four of them being 'combinable' for two full-height drives. Two more bays are available for 3,5-inch drives; one of them is occupied by the floppy. Except for the two bottommost bays, all are accessible. Eight sockets are available for 72-pin SIMM modules. They have to be filled in pairs, and the memory controller uses the parity bits for ECC. All eight MCA slots have a width of 32 bits. The planar however does not have a video card; mine came with a simple IBM SVGA Adapter/A (512K VRAM, maxes out at 640x480x256). I replaced it with an XGA-2 card, giving 1024x768x256 or 800x600x64K both for Linux and OS/2. Finding other cards is difficult, since most of them rely on an on-board VGA adapter the 85 does not have.

Unlike to its predecessor, the case is made of metal instead of metalized plastic: there's no problem in sitting or standing on it (in fact, already the 80's mechanics were good enough to carry a human; you are however feeling far more secure if your personal 100 kilograms are carried by solid steel instead of plastic...).

A nice detail not found on many machines: the power switch is covered with a slider that avoids turning it off accidentally. In general, this is another fine example how well thought-out cases can be built if they don't have to be optimized for the lowest price. To bad you only find this in high-end machines...

The SCSI adapter is a fast/wide adapter, allowing data rates of up to 20 Mbytes/s, similar to the 'Corvette' Fast/Wide SCSI Adapter. You just don't have the extra channel for external devices...

Opening and disassembling the Model 80 was already easy; you only needed a coin or screwdriver to remove the side cover. For the 85, you even don't need that:

Opening PS/2 Model 85, Step 1
Opening PS/2 Model 85, Step 2

First, pull off the front cover and slide off the side cover. To add or remove cards, you're already done at this point...

Opening PS/2 Model 85, Step 3
Opening PS/2 Model 85, Step 4

...otherwise, snap off the inner metal holder for the drive bays. To get access to the memory module sockets, finally swing out the power supply. Contact between supply and planar is via a special connector that automatically unplugs. A fine solution to avoid a cable that gets bent every time the supply is swung in or out! However, this principle wasn't applied to the drive power connectors; at least, they're long enough and plugged at the supply's side.

Visible at the side of the drive bay frame are a couple of microswitches; they can detect whether the machine is mechanically locked via the keylock at the front side, and whether the machine has been opened. Such locks are needed to build systems with C2 certification.

Photo of IBM PS/2 Model 85's main board
Click here or click onto the photo for a full size version of this picture.

A look at the 85's main board. This is a newer release that has a 486DX2/66 CPU; first-generation 85's had a 486SX33. The SCSI cable is like all cables should be (ribbon cables are also good, but this one is better): all wires are twisted pairwise. Such a configuration would even be good for Ultra2-SCSI, but it gives an additional level of reliability for standard (slow ;-) SCSI.

However, the SCSI connectors are again IBM proprietarity at its best: 68-pin mini Centronics connectors are a nightmare to get, especially for external devices. This machine only has a narrow internal cable, and a special adapter transforms the mini Centronics connector to a 50-pin edge connector; still not very standard-conformant, but at least the same as for the older narrow SCSI controller cards made by IBM....

Intel i486DX2 @ 66 MHz
integrated into CPU
8K internally in CPU, 256K L2 cache module
64 Mbytes (options range from 8M to 256M)
8 MCA slots (32 bit)
Interfaces (onboard):
  • Mouse, Keyboard
  • 1 x Serial
  • 1 x Parallel
  • Floppy (2.88M), allows attachment of up to 3(!) drives
  • SCSI (wide)
Add-on cards:
  • 3COM 3C529 Ethernet Adapter
  • IBM XGA/2 Graphics Adapter
Operating System(s):
  • OS/2 Warp Version 3
  • Caldera OpenDOS 7.01
  • Linux 2.2 (Slackware-based)
Useful Links:

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©2001 Alfred Arnold,