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IBM PS2 Model 90 XP 486 Technical Reference (October 1990)

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The IBM Personal System/2 Model 90 XP 486 Technical Reference, First Edition (October 1990), is IBM's 96-page model-specific hardware and software interface reference for the PS/2 Model 90 XP 486 (8590), the desktop 486 Micro Channel machine with a removable processor complex.

What it contains

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  • Section 1, System Overview — system board features, the I/O address map, specifications and the power supply section.
  • Section 2, Programmable Option Select — the POS registers and setup.
  • Section 3, System Board — Micro Channel implementation, memory, RT/CMOS RAM and system control ports.
  • Section 4, Processor Complex — this section does not exist in the earlier PS/2 technical references. The 90 and 95 carry the processor, cache and memory controller on a replaceable complex, and this chapter documents its components and interface.

Physical specifications: 440 mm wide, 430 mm deep, 140 mm high, heat output 329 W (1125 BTU/hour).

What it does not contain

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This is a programming and interface reference, not a service manual. There are no FRU part numbers, no removal and replacement procedures, no symptom-to-FRU index and no component values — IBM put those in the model's Hardware Maintenance Reference and Hardware Maintenance Service pamphlets. There are no schematics; the planar is described as a block diagram and a set of register and connector tables.

It is also not self-contained. IBM split the PS/2 Technical Reference library into volumes, and this one carries only the model-specific part. Anything common to the family — Micro Channel architecture, the serial and parallel port controllers, the instruction sets, the keyboard scan codes — is in the Hardware Interface Technical Reference volumes, and BIOS in the BIOS Interface Technical Reference.

What it settles

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  • No −5 V rail: "the system-board voltages are +5 Vdc, +12 Vdc, and −12 Vdc", with +5 Vdc and +12 Vdc to the internal drives.
  • The processor complex is a field-replaceable subassembly on this model, which is why a dead 8590 is not necessarily a dead planar.

Download it here: IBM PS2 Model 90 XP 486 Technical Reference Oct90.pdf

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