The Model 90 is the desktop equivalent of the model 95, in the sense that it also uses processor complexes instead of a CPU integrated onto the planar. However, IBM dropped this concept for desktops and the 90 later got replaced with the Model 77, a PS/2 machine with a 'monolithic' planar. Therefore, the 90 never was shipped with more than a Type 2 complex, but it is still possible to put in Type 3 or Type 4 complexes as upgrades. With a recent Type 4 complex and an upgrade adapter socket, CPUs up to a Pentium 233 would be possible...

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Probably due to space constraints, the 8 memory SIMMs are also located on special raiser cards. The Type 1 complex requires memory in pairs, but since modules that belong to the same pair are located on the same raiser, one can get along with only one raiser in the machine.

IBM put special effort in cooling the machine. A second fan in front of the cards assures that they get cooled enough even when all slots are full, and a special plastic baffle directs a part of the airflow towards the CPU module. As a result, the i486DX doesn't need an extra heatsink.

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The Type 1 complex came in a lot of varieties, ranging from a 486SX/20 to a 486DX2/66. Technologically, it is a relatively old complex. It still uses the metal-canned chips known from the first generation of PS/2s that were abandoned in later models, like the Type 2 complex. A Level 2 cache was an option, but it was rarely used: So far, I have only one Type 1 complex with the cache option...

Processor:

Intel i486DX @ 33 MHz

Coprocessor:

integrated into CPU

Cache:

8K internally in CPU, optional 256K cache module

Memory:

16 Mbytes (options range from 4M to 64M)

Bus:

4 MCA slots (32 bit)

Interfaces (onboard):

• Mouse, Keyboard
• 2 x Serial
• 1 x Parallel
• Floppy (1.44M), allows attachment of up to 3(!) drives
• XGA Graphics Adapter

Add-on cards:

IBM SCSI Controller with Cache (2MB)

Boca Parallel Expansion Card

IBM 16/4 Token Ring Adapter

Operating System(s):

• currently none

Useful Links:

• Original Announcement from IBM
• Details about main board
• Details about processor complex
• Reference Diskette
• Diagnostic Diskette