Where to begin...

So the IBM PS/2 Model 95 series was the last in the 'PS/2' range introduced in 1991 (even though IBM would continue to release other Micro Channel based systems in their RS/6000 line, as well as beefier servers like the PC Server 500. There were also some late servers that combined PCI and MCA). Essentially these found use as light servers or workstations-- I do not know of any home users purchasing one for the incredible price tag back then.

There are two types of model 95s. The first revision (which some model '85' systems were converted into: you can tell if they have a silver IBM logo instead of a blue one-- plus the PSU won't be the 400 watt variant) and the later 95A types. Although some first revision 95s may also have the 'A' designation if it's related to the RAID configuration, I'm not entirely sure.

1. The first revision 95s are able to run more types of complexes but have slower throughput. They have a single parallel port, and a single 'old school' serial that needs an adapter to bring it to 9 pins.
2. The later 95s can only run Pentium complexes. They feature a reworked operator panel with the power button on the left, along with introducing a HDD activity LED (yeah unusual that the first revision didn't have that). And of course two 9 pin serial ports and two parallel ports.

What's a complex? It's essentially a modular CPU card. There were complex types from type 0 to type 4. Type 0 was the only 386 complex (and reportedly has problems running in first revision model 95s-- since I don't own an example of the complex, I have not been able to determine if it IS possible to get working). Type 1 through 4 had various renditions of 486, and of course only the Pentiums were featured on the Type 4 variant. Basically the 'type' (regardless of CPU architecture) defines characteristics like L2 cache, memory type supported, IML behaviour, and other things. According to IBM the type 1 complex was the *first* device to sport the DX-50.

IML stands for 'Initial Machine Load' (a bit of a spin-off from the AS/400 IPL 'Initial Program Load'-- similar error code behaviours too). It basically contains the BIOS functions for PS/2 computers and on most is stored on the hard drive--with the exception of the Type 4 complex which stores everything in flash. Now the type 4 complexes can store a backup copy of the IML partition on the hard disk, but it [IML partition] is not necessary for operation of the system.

One notable aspect about the Pentium based complexes is that the use SynchroStream for advanced caching, and also can use up to 256 MB of *SIMM* memory without performance penalties (like regular systems which lack the 11-bit RAM tag).

With that lengthy introduction out of the way, my PS/2 Model 95 project was something that was never meant to be, but happened. Due to a disturbance in the cosmos three model 95s appeared on ebay, and I selected one that I would give a crack at to work on being pretty cheap. It had a 486 complex being a first revision—so I had to quickly source a Pentium complex, RAM (due to the fact the Pentium complexes use different SIMM types), SCSI CD drive, as well as a better SCSI controller. The system was being sold as parts or as a ‘suitable movie prop’ due to the fact it was shooting error I999 0301 for ‘no bootable device’, which is a common error on any system. But not so easy to fix on a PS/2 like this…

I began research on a better SCSI controller that could address U320 drives. It appeared that on all of IBM’s later “fast wide” SCSI controllers, they use a mini-centronics 68 pin to regular 68 fast wide pins (for the receiving end of the cable)… which means you’ll *never* find a cable like that unless you purchase the specific FRU from IBM. This is something IBM carried on into their x Series strangely enough. So with that unfortunate discovery, I purchased a nice long U320 SCSI cable—along with a min-centronics 68 pin connector to manually crimp on…

Typically you see 80 pin mini-centronics connectors on hot swap HDDs, but rarely the 68 pin variant in combination with a regular 68 pin high density SCSI connector… yeah the two are interchangeable, but needlessly so. I suppose IBM’s logic is that the mini-centronics connectors make better contact and don’t have tiny pins to worry about.

So after a good half hour fiddling with the cable, I got the mini-centronics portion crimped on. Smacked it on with a hammer once I had it oriented (which by the way I wasn’t paying attention to, I *just happened* to hammer it in on the correct orientation):

The reason why I am also using the 50 Pin cable (which uses card-edge to regular 50 pin breakouts) is because the CD drive is a regular 50 pin, and it’s just easier to have that running on its own cable. That weird card-edge to 50 pin cable was made by DuPont…

You can see the SCSI cables slinking everywhere, along with the crazy blue receiving connector from the giant swing-out power supply:

After putting a new CMOS battery in, I had to feed the system all of the ADF files so it could properly use all of the cards. Next problem installing Windows 95… Windows 95 is too stupid to see the SCSI drive, and trying to find the particular drivers to inject in for it to see it properly, is just a pain in the butt. We also have to address the fact that the type 4 complex in combination with the SCSI controller cannot deploy the IML “convenience partition” to a drive greater than 3.94 GB. So I took a regular U320 15K 74 GB SCSI drive and re-sectored it down to 3.90 GB (or 8171520 sectors) on a special computer which had DOS as the application was DOS-only. Then it hopped back into the PS/2 to get an FDISK and the IML partition deployed. Then it went into a third computer to have the FAT32 partition re-created (because for some reason Windows 7 can’t recognize it with FDISK in the 95 boot diskette…) thankfully this does not destroy the IML partition. Then I put in the 95 installation files. It’s actually handy having the whole windows 95 image reside on the hard disk because you don’t have to put anything in when the “insert disk for change X” appears—it just runs automatically. Then we go back into the 95 boot diskette and run SETUP with “/id /im /it /is” (which makes it go faster). After all of that, the installer worked and we’re in Windows.

“But it’s an MCA system, you’re nuts because there’s no way you'll get audio”
Well I did manage to hunt down an MPU-IMC along with an MCA Sound Blaster. So this PS/2 Model 95 can do OPL2, PCM audio and MT-32 output without a sweat; a rather uncommon thing for an MCA computer admittedly. However with a previous thread I created—the MPU-IMC simply won’t work with a small selection of games, from my testing it seems to be an address problem (Mau1wurf says it could be with the IRQs, however, the games that don’t work don’t demand IRQ 2/9, but you never know! Not many people bring up the MPU-IMC). I guess one workaround is to also use softMPU on it.

“But Microchannel cards don’t play nicely in faster PS/2s”
After reviewing on WHAT caused the timeouts and slowdowns on MCA soundcards, it turns out OEMs were using low schottky chips. Replacing the ‘LS’ schottkys with advanced (ALS) or fast (FLS) resolves the problem. You have to replace ALL of the LS chips. You’ll notice the model 95 motherboard itself will have ‘ALS’ surface mount chips. I just recommend using ALS for everything when dealing with MCA…

Here’s what I have presently in the machine, I put some green lighting in too:

Inside: F/W IBM SCSI Card, SMC Ethernet (soon to be replaced by an IBM Ethernet LAN/A card which is the fastest MCA Ethernet card made), MPU-IMC, Sound Blaster MCV, XGA-2 (soon to be replaced by the SVGA cirrus card called delivery boys 2.0 by IBM),

And here's the little MT-32 perching atop the Model 95-- I will soon have a "revision 1" buddy for it:

It's so totally awesome to use this computer in the dark:

And here is the final setup, I had to swap in my 22" CRT because the mini 15" IBM one is currently in pieces awaiting for a recap-- you can also see the red pentium sticker at the lower right of the bezel that I put on:

Running 320x200 on a 22" CRT is just my favourite! Seeing the awesome scanlines, coupled with perfect contrast, and fast instant phosphor response:

Unlike most who use CRTs, I *love* 60 Hz. However if you have a cruddy CRT, chances are 60 Hz won't have a proper persistence ratio. 85 Hz makes me uncomfortable. There *are* CRTs which run at 60 Hz kill me, but I don't own any of those...

Present Specifications:
CPU: Socket 4 Pentium @ 60 MHz
RAM: 64 MB (4x 16 MB parity SIMMs)
2.88 MB FDD
2x SCSI CD-ROM

And of course, all of the aforementioned MCA cards.

Well that's pretty much it. I do have a few more things I want to get this system set up with-- but they're still in the works. Because I like dedicating certain computers roles, this one is my exclusive MT-32 computer. And the OPL2 it outputs is perfectly silent due to the advanced grounding. The motherboard and the power supply will be getting a complete recap at some point.

I admit this required an unusually in-depth mix of hardware and software knowledge, but it's a fun computer now-- so that's all that matters. It originally had a bunch of specialized MCA phone cards and ran OS/2 WARP (boring business stuff).