386/40 - Fun, Frustration, & Taking It To The Next Level

 One of the computers I wanted to add to my retro computing collection was a 386. My initial plan was to find a period correct case and then just build it out from there. I made a post on the Vintage Computer Forum asking for such a case. A forum member, who is a recycler, reached out to me he may have what I was looking for. It turns out he had complete systems. I picked the one I liked which he told me that one was a 386. To my surprise when I got it was a 386/40 in nearly perfect condition. I upgraded the memory to 8MB, added a Cyrix FasMath math coprocessor,  XT-IDE CompactFlash adapter, Tseng Labs ET4000AX video card, Sound Blaster 16 sound card and 3Com 3C509B network card. I replaced the AMD 386/40 CPU with Cyrix 486DLC/40 CPU.

I thought I was all set, but then problems began to set in. I could not get any protected mode games like Doom to run. They would just start up and then quit. I could not load an extended memory manager like EMM386 or QEMM386. I would get protection faults. I put the 386/40 CPU back in and that helped some, but the problems continued. I ran memory tests with CheckIt 3.0 and came up Ok. Trying to run the System Board test with freeze on the protected mode tests. I was beginning to the think the board was not in working order. I switched some the memory around and when running the System Board test, I finally got through it, but it reported parity errors. It turned out the 30-pin SIMMs I was using are not all that compatible with 386 motherboards. I decided to replace the 3 chip 30-pin SIMMs with 9 chip 30-pin SIMMs as these are more compatible. That fixed the problem, and I could now run protect mode games and utilities again. I put the 486DLC/40 chip back in and problems started happening again. I ran diagnostics and it turns out that something was going on with the built in 1K L1 cache on the CPU. Disabling the 1K L1 cache fixed any issues, but that would slow the computer down to almost the same speed as when I had the 386/40 CPU installed. Now these Cyrix 486DLC chips are known to have cache coherency issues with a lot of 386 motherboards, but this motherboard had 486DLC marked on the CPU socket and recognized the CPU properly on the BIOS post screen. I tried enabling the 1K L1 cache using the Cyrix utility instead of doing this in the BIOS, as this is supposed to be more compatible. This did not help. I decided to take a chance and get a different 486DLC/40 CPU. This one worked and I have had no further issues. This finally ended weeks of frustration.

The Cyrix 486DLC CPU takes a 386 system to about as fast as you can go. How much faster? Here some benchmarks from Phil’s Computer Lab showing the results:


You will not get a doubling of performance, but I got a nice performance boost that matches the above results. For a more in depth look at this CPU upgrade, here are links to Phil’s Computer Lab and Ancient Electronics on this topic:

https://www.philscomputerlab.com/cyrix-486dlc.html

https://ancientelectronics.wordpress.com/2016/08/04/upgrading-the-386-enter-the-cyrix-486dlc/

I am really enjoying this computer. It brings back so many memories of having a 386 and what that time in computing history was like. Lastly here a few pictures of my 386/40 computer.




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