Shipped on Dec 13, 2024 from Lohja in Finland, the package found its way to Sunnyvale in USA on Dec 23, 2024. I was happy to see the seller had put the box in a box as we had agreed. Everything looked like it had arrived in pristine condition.
My 2168-594 box is not exactly an eye-catcher. Each PS/1 had variants named Consultant, Expert, Essential, and Investor depending on where they were sold[1] (Consultant = General Merchandiser, Expert = Computer Stores, Essential = Office Superstores). The Consultant version has a very appealing box likely aimed at capturing customer's attention. My version is likely an Expert variant.
At first sight, the machine looked in very good condition. We will see it was not quite so.
I was overjoyed to have scored all the original manuals (start front, start back, assembly, Know your PS/1, Adding Options, and Maintenance Manual). Having grown up with second hand hardware, getting both the box and the manuals were a huge step up.
The "Adding option to your IBM PS/1 computer" document is so gorgeous that I scanned it.
This computer may have had a French owner at some point. The manual's last pages features a French phone number from Evry (near Paris) and mentions upgrades in Francs (Pentium = 1590F).
The euphoria was short lived. Taking the central unit out of the box revealed rust spots that were not visible in the eBay listing.
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| What I bought | What I got |
I decided not to put that on the account of malice. What likely happened is that the seller took photos of the machine before leaving it in storage until it sold. At least that is how I made peace with the situation.
As long as the machine could boot, I felt I could fix it. I plugged everything in, flipped the power supply from Europe's 230V to US's 115V, and pressed the power button. This is what I witnessed next.
Despite the rust, it was alive! But what would it look like under the hood?
To get access to the inside, the manual instructed to slide the metal cover forward.
I tried the maneuver, progressively increasing the strength but it did not move. At some point I worried I was going to break the handle. After what felt like an eternity I realized the CD-ROM in the front was too large for the case and acted like a clip. There was no other way but to push harder and pray I did not break the plastic frame.
I ended up pulling on the case while pushing on the CD-ROM super hard. While I was unhappy about that cut in my hand I was pleased the case opened without breaking!
To my horror I found a lot more rust inside. It looked scary but nothing structural was impacted. The electric components looked ok. It was time to pop open a bottle of WD-40 and get to scrub.
Front before
Front after
Top before
Top after
Botton before
Bottom after
 Back before
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 Back after
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I eventually got the back completely rust free but found it difficult to scrub without damaging the stickers. A few more months and that PC would have been unsalvageable.
The inside was typical of a '90s PC. Namely a mess of dust, ISA cards, cables, and wires.
I started by removing all the ISA extension cards. I did not see a video card in the bunch. It seems IBM integrated it to the motherboard.
Notice the stamp on the bottom of the case. This machine was assembled on Dec 20th, 1993! I also removed the riser card to get full access to the motherboard.
With a better view of the motherboard, I could establish that it was a 2168A (TYPE 1). theretroweb.com has a nice drawing of it along with a list of all the chips on the motherboard. I noticed a Socket 2 (PGA238) meaning there was potential for an upgrade from 486 to Pentium.
The CPU was still the original DX2-66Mhz. The L1 cache was also the original 128 KiB (quite a good amount for the time). The VRAM (1MiB) was already maxed out with a soldered VRAM chip. I got a nice surprise with the RAM since it found an insane amount for 1993. The original 4 MiB had been increased to 32 MiB!
In the image above, four MT5C256B (32KiB) SRAM chips make the L1 cache. There is a TAG chip (MT5C640B) of capacity 16KiB which is part of the L2 system. It will be discussed extensively in the upgrade section.
Also notice on the same photo, the 1893NDK37 crystal oscillator with, just below, the IMI SC418DXB which sets the motherboard frequency. Epictronics has a nice video about it[2]. The motherboard frequency is set via resistors instead of jumpers (and that is why I really wanted a 33Mhz system). Also notice the awesomeness of the Vogons community and in particular user thermalwrong who managed to find the chip datasheet[3].
The original 253 MiB IDE HDD had been replaced with two hard drives, one of 1GiB and one of 1.6GiB. I was surprised with these capacities. During my research I had established the BIOS on the PS/1 did not have Logical block addressing (LBA) support. This means it should have been limited to 512 MiB HDDs.
It turned out there is a software way to go beyond the lack of LBA called Dynamic Disk Overlay (DDO). My machine came with something called OnTrack, licensed by Western Digital[4].
I had no use for it but did not want to be left with a gaping hole in the front panel. I hesitated between a Drawer storage and a Kingwin KF-22-IPF Aluminum IDE Mobile Rack. I went with the Kingwin because it has a more '90s feeling.
There were five extension ISA cards in the machine. One was a hand scanner connector, one was a modem, one was a SCSI port. I had no usage of them. I only kept the last one which was a Pro Audio Spectrum 16 (650-0060-52-D) sound card.
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There was no marking on the front of the CD-ROM drive. It looked like it used a caddy loading system. It is really too bad the tray became the dominant form factor back then because caddy are both more elegant and cooler. I was able to assess this drive was a NEC CDR-84JD-1.
Given how that drive made opening/closing the case difficult, I knew right away I was going to have to replace it.
Reminder of how ad-hoc everything was back in those days, the "LINE OUT" of the CD player had to bypass the CPU and be directly connected to the sound card.
With the hardware inspection done, it was time to run some software to learn more about that PC. I tried HWINFO.EXE but found ASTRA outputs far superior.
The integrated Super VGA chip was confirmed to be a Cirrus Logic GD5428 with a generous 1 MiB VRAM (quite a high amount for 1993). According to dosday.co.uk this chip was the sign of an high-end card[5].
I was relieved to confirm the graphic card was mounted on a Video Local Bus (VLB) instead of ISA. One of my goals with this restoration project was to max out DOOM at 35 frames per second. I knew that an ISA video bus would have made that impossible to achieve[6].
Here are more ASTRA insights about the BIOS, Master disk, Slave disk, Sound, and Video.
By 1993 the world of Super VGA was getting organized. The VESA group had agreed on a video standard to go past VGA. This Cirrus Logic came out too early to get the most important VBE 2.0 and its Linear Buffer. It only supports VBE 1.2 which still allows some games such as Duke 3D and Quake to run at 640x400 (at an abysmal framerate).
Something really cool about these IBM PS/1 is that you don't need to restart the computer and hit F2 to access the BIOS. Instead you can run the command CONFIGUR.EXE from the DOS prompt at any time.
There is not much there. You can't overclock anything or set the RAM timing. BIOS started to become awesome in the late-90s. Notice however the ability to disable the cache which was handy when I benchmarked the impact of L1/L2 later in this series.
Overall, and despite the rust, I was happy with my purchase! Besides embodying the best configuration money could buy in 1993 (VLB, 486DX2 66Mhz), the machine has been upgraded with a 16-bit sound card, 32 MiB of RAM, 2 GiB HDDs, and even a CD-ROM drive!
CPU : 486 DX2 66 Mhz L1 Cache : 8 KiB RAM : 32 MiB L2 Cache : 128 KiB VRAM : 1MiB Video Chip: Cirrus Logic GD5428 Bus : Video Local Bus HDD : WDC AC21600H 1.6 GiB HDD : WDC AC31000H 1.0 GiB Sound Card: Pro Audio Spectrum 16 model 650-0060-52-D (SCSI) CD-ROM : NEC CDR-84JD-1 SCSI 2x
With the unboxing done, it was time to add personal touches, starting with a keyboard.
