My Computer Collection
IBM PS/2 Model 95 (486/66 Type 4 Complex)

Photo of IBM PS/2 Model 95
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This is a member of the 'second generation' of Model 95 machines, notable by the model number 9595 opposed to 8589 for the older machines. There are basically two sorts of 9595 systems: The 'older ones' that use the older Type 1..3 processor complexes and the old 8595 planar, just with a 2.88MB floppy drive and maybe an XGA-2 card (similar to the 8590-->9590 upgrade). This is an example of the newer 9595 systems that have been redesigned significantly. On the front side, they can easily be identified by the different layout of the operator panel: the LED display moved from the left to the right side, and there is now an extra LED for HD accesses...which unfortunately stays unused for the RAID-based Server 95A systems, like this one...

Photo of IBM PS/2 Model 95's back
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The back side of the machine reveals some more of the improvements of the redesigned Server 95 planar: There are now two serial and two parallel ports. The first parallel port is capable of DMA-based transfers, while the second one is a 'normal' bidirectional port. Inner values are the support for synchrostream transfers and support for 40-bit wide RAM modules, allowing on-the fly correction of single bit errors in ECC mode. Thankfully, simple parity mode is still possible, since ECC SIMMs are virtually unavailable in the second-hand market...

Photo of IBM PS/2 Model 95's RAID cages
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A closer look on what is signified by the 'A' in the 'Server 95A' name: the 'A' stands for 'Array', which means that the machine is equipped with a hardware RAID. The two bottommost drive bays are populated with cages that can hold up to three hard drives of one inch height. This is the smallest configuration available: only one cage is filled with drives (the other one only contains plastic dummies that assure proper airflow), and the drives are 540MB Maxtor models. They form a RAID0 array of 1.5 GBytes. To remove a drive, turn the corresponding blue knob with a screwdriver.

Photo of IBM PS/2 Model 95's RAID controller
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The RAID controller is the so-called 'Passplay' variant and is based on a Mylex DAC960. As the name implies, the onboard processor is an Intel i960 RISC controller. Two independent wide SCSI channels are available, with each usually driving a separate RAID cage. The controller however is not limited to disks in arrays; you may also attach single devices to the bus (like the CDROM in this case) and they also show up as-such on the host side of the controller. Arrays of drives of course show up as a single hard drive...

The 4 SIMM sockets may be filled with either 1M, 4M, or 16M 30-pin SIMMs. In contrast to the older cached SCSI adapter ('Spock'), they are of the industry-standard type and do not have the different CAS-layout of the IBM-style modules. Extending the cache to more than 4MB is therefore simple, but in practice, it doesn't give any speed adavantage except for constellations with several RAID5 arrays. Consequently, the successor of the Passplay ('Cheetah') did not allow extension of the 4MB.

Photo of IBM PS/2 Model 95's CPU Board
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This is the smallest one of the Type4 complexes, the type of processor card required to operate a Server 95(A) planar. All Type4 complexes have in common that they use an Intel cache controller for the L2 cache. A relatively expensive solution, but who cares at IBM's prices ;-)

Intel i486DX2 @ 66 MHz
integrated into CPU
8K internally in CPU, externally 128K L2 Cache
32 Mbytes (options range from 8M to 64M)
8 MCA slots (32 bit)
Interfaces (onboard):
  • Mouse, Keyboard
  • 2 x Serial
  • 2 x Parallel
  • Floppy (1.44M), allows attachment of up to 3(!) drives
Add-on cards:
  • IBM RAID Controller ('Passplay' Variant)
  • IBM SVGA Adapter/A
  • IBM Fast/Wide SCSI Adapter
  • IBM 16/4 Token Ring Adapter
  • Operating System(s):
    • Caldera OpenDOS 7.01
    • OS/2 Warp 4
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    ©1999 Alfred Arnold,