View Full Version : IBM PS/2 model 55sx

February 12th, 2010, 01:50 PM

Processor : Intel I386sx 16/32 bit running at 16 mHZ
Standard co-processor : Intel I387 16 bit running at 16 mHZ
Memory : 1-8 megabytes depending on options installed
Expansions: 3 Micro Channel-Architecture IBM proprietary bus slots
Standard on-board interfaces: 1 PS/2 mouse, 1 PS/2 keyboard, 1 serial (RS-232), 1 parallel, VGA monitor connection
Internal interfaces: IBM proprietary floppy 34 pin connection (NOT IDE), DBA connection for ESDI HDD
Operating systems supported: OS/2 (and warp), MS-DOS, PC-DOS, Windows
Information of interest

The IBM PS/2 model 55sx was IBM's attempt at a mid-range computer for business and professional use. The 55sx was the first IBM computer to utilize a 32 bit processor and contained a 16/32 bit Intel I386 processor soldered to the mainboard. If installed an extra coprocessor would usually be an Intel I387 though there were other processors which were installed depending on the time of purchase.
Possible Expansion

The IBM proprietary Micro channel architecture was IBM's attempt to utilize newer technology to overcome several of the problems from the PC bus (later known as ISA). Sadly the MCA (micro channel architecture) never caught on with PC manufacturers and was soon replaced by PCI. During the time when MCA was more common however a large variety of boards were manufactured including Ethernet, processor accelerators, Memory expansions, sound cards, dial-up, ect.
Things to note if you plan to acquire a 55sx

Initially the 55sx was one of the most common computers in the PS/2 line although there are several problems with it that has reduced it's numbers in more recent years. The 55sx has an error usually solved by replacing the CMOS battery (error 161) however in the 55sx rather than a CMOS battery IBM used what is known as a Dallas clock module (DS1287). This clock module had an integrated battery which kept the clock and BIOS running. This battery would eventually fail however and Dallas semiconductor no longer manufactures this device. The DS12887 is the immediate successor to the DS 1287 and unlike it's precursor is Y2K and Y2K38 compliant, it is also the only modern version of this device which is still usable in the 55sx. The DS12887 is sadly also out of production though it is somewhat easy to find and is still somewhat common. Rework on both of these modules may be done as illustrated here: http://www.youtube.com/watch?v=QbKLMWlBd3s (Please note that the person in the video is not myself).