RAM speed for 386 machine \ VOGONS

RAM speed for 386 machine

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First post, by walterg74

Posted on 2020-01-15, 20:26

walterg74 Offline

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I am looking at 2 386 boards I have, one has a 386Dx-40, with FPU, and 128KB cache. The other has a 386SX-40, no FPU of course, and no cache on the board.

Mem results with the cache check of course show a vastly superior speed for the DX board, but for the rest of the RAM the SX is slightly above the DX.

I checked the main RAM but the SX seems to have 4 70ns SIMM modules (maxing out it’s 4 slots) and the DX also has 70ns SIMM modules, filling up 4 of the 8 available slots.

Numbers seem to be about 8.9MB/sec for the DX vs 9.8MB/sec for the SX.

Does this make sense? Would either benefit from faster RAM?

Reply 1 of 4, by H3nrik V!

Posted on 2020-01-15, 20:41

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The sx/dx names on 386 doesn't specify fpu or not. That is the external databus' width .. A 386sx can work together with a 387sx, where as the 386dx uses a 387dx ..

If it's dual it's kind of cool ... 😎

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Reply 2 of 4, by cyclone3d

Posted on 2020-01-15, 20:42

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What are the RAM timing settings in the BIOS of the different boards? Do the motherboards have the same chipset?

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Reply 3 of 4, by walterg74

Posted on 2020-01-15, 20:56

walterg74 Offline

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cyclone3d wrote on 2020-01-15, 20:42:

What are the RAM timing settings in the BIOS of the different boards? Do the motherboards have the same chipset?

Didn’t check, will take a look.

Different boards/chipsets.

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Reply 4 of 4, by mpe

Posted on 2020-01-15, 20:59

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DX should be faster given twice as wide data path to the memory. Supposing you are testing 32bit transfers (which was not common in DOS). Depends on how you test.

If testing 16bit, thenthings like waitstates or memory interleaving in the SX board could favour the SX.

Faster RAM would only help if you can control RAM timing or wait states (in setup or by a jumper). A simple replacement of RAM chips for faster without changing anything else won't help.

The impact of faster RAM will be much higher on the cache-less 386SX.

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