386SX/40 Build - The Fastest 286 I Have Ever Owned
The title of this blog post may sound a little misleading, but it is in fact the truth. You see the 386SX would have never come about had it not been for the popularity of the 286 and Intel did not like that popularity. Many companies had a license to produce the 286 chip and most of the chips sold were from companies other than Intel. That negatively affected their bottom line. When the 386 came out in 1985, Intel decided not to license it to anyone else, so all sales of the chip would end up in their coffers. The 286 continued to sell like gangbusters and the 386 was just too expensive for most people, so what was Intel going to do about it. Intel came up with the 386SX in 1988 and it was to the 386 just as the 8088 was to the 8086. A less expensive version that could be used in existing 286 systems with just a few modifications. The 386SX differed from the 386 in two ways. It only had a 16-bit versus 32-bit data bus and was limited to 16MB of memory versus 4GB. This made the entry into 32-bit computing a whole lot cheaper. Computer and motherboard makers pounced on the 386SX and Intel succeeded in finding something to have as an alternative to the 286. The 386 was renamed to the 386DX to differentiate between the two CPUs. The stranglehold that Intel had on the 386 market would come to an end in 1991 when AMD's reverse engineered 386 clone came to market. The CPU in my system is in fact an AMD 386SX/40.
The TD70AN board I have is typical for that the early 1990s era. It has 1 8-bit and 5 16-bit ISA slots and 4 30-pin SIMM sockets. It does not have any cache memory and the majority of 386SX boards did not as well. I obtained the board from a seller on eBay for only $50 with the extra added bonus of the barrel battery being replaced. The one issue I had when I got it is that the time of day would not update when when powered off. I later found out that the 2 middle pins of the 4-pin connector labeled CN7/EXT BAT needed to be jumpered. I tried using 16MB of memory in this board but ended up having compatibility issues. Here is my final configuration
TD70AN 386SX/40 motherboard with AMD 386SX/40 CPU
IIT 387SX/40 Math Coprocessor
4MB (4x1MB) 60ns 30-pin SIMMs
Paradise WD90C31 1MB ISA video card (It has 2D acceleration for Windows 3.x)
Sound Blaster 16 CT4170 ISA sound card
3Com Etherlink III ISA network card
Goldstar Prime 2C Multi I/O card
Lo-Tech XTIDE card for large HD support (Only the BIOS is used for this and is shadowed)
Compact Flash to IDE adapter with 2GB Compact Flash card
MS-DOS 6.22 with Windows 3.11
You may notice one thing about this computer. The case looks almost identical to my 486 Pentium Overdrive build and you would be right. I moved that system to a brand new mid-tower case and used this one for the 386SX/40 build. The thing that is different is that I found a replacement button cover for the Turbo switch. I really was lucky to find an exact replacement and it does make a difference in the ascetics of the computer. I have a 386SX/16 and a 286/12 computer and while those are a lot of fun I prefer having this 386SX/40 system instead. It covers a lot of ground in the software it will run through use of the Turbo button. It was just one more of those bucket list systems I wanted but never owned and I could not be happier with how this build turned outed. Finally a few pictures.
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