well, I don't think it's going to be really that much difference, but... First I remember reading somewhere that 40mhz cpu should have 60ns otherwise it's working in wait states. But the most tempting reason to try it, is that I have already 6 60ns simms, and I need a couple of more to have 8 😀

You don't require to have 8 to try, 4 should be fully sufficient.
My 386DX-40 runs with 2/0 WS, though I can't tell definately how fast the SIMMs are I have built in.

If you do get around to upgrading post some before/after benchmarks. 😀

elianda I know that, but I want to have 8MB on that pc, plus that I really use it, and I want to have it fixed as soon as possible, so as not to open it every once in a while. Mostly because I have very limited space, and every time I need to open to fix something I have to move a lot of things. As for the benchmarks, it is very easy, as I can use one of my spare 386/40 bords, and 4MB. Any suggestions on which benchmark to use? Thanks!

I was going to suggest Doom but wouldn't it be I/O limited with 4MB?
Also the graphics card matters too from what I've read.

What about memtest86?
That should run on a 386 and IIRC provides memory transfer speeds.

It might be good to have 8 matched SIMMs installed rather than four. Some of the better motherboards support memory interleaving, which requires all 8 SIMMs be installed on a 386DX/486 motherboard.

It is fairly uncommon on 386 systems, but not non-existant. For example, I have an American Megatrends 386SX board (not just the BIOS, but the actual board) that supports memory interleaving, and it is a huge improvement on what you would get on a normal 386SX board.

yes, I've heard that. If I remember well, memory interleaving was used in some low end 386sx motherboards to compensate for lack of cache memory? By the way, I have a board with an AMD386SX/SXL-25, with no cache at all. By looking it's specs, there is a block of jumpers that control "Pipeline Mode Configuration" and options are enable/disable. Do you think it might have to do sth with that?

My 386sx board is fortunate enough to have both cache and interleaving. It's surprisingly fast for what it is.

I have not heard of anything called "pipeline mode configuration" on old boards before. One way you could test your theory is to run a memory benchmark before and after. If it interleaves, you will see roughly double the throughput.

I had no luck with memory benchmarks today... I had in mind to test the ram on my 386/40 using first 70ns simms and then replace them with 60ns and repeat the process. I tried first memtest86, which run ok, but displayed no memory speed info at all (as opposed to my pentium where it said many more things....). A couple of other ram benchmarks I found, would either hang or reset the system(again on my pentium they work fine.....). Now about the "pipeline" thing of the old 386sx, I measured the speed with it enabled and disabled, and found out that with having it disabled, it's a little faster, so I leave it there... 😀

Assuming the CPU speed and number of wait states are held constant, I don't see what good having faster memory will do.

A 40MHz CPU has a cycle time of 25ns. Subtract 10ns for decoding and buffering and you would need 15ns DRAM in order to run zero wait states. This is where SRAM cache comes into play, as it can make your system feel like it has 0ws during certain operations. Not that 40MHz 386s usually have 15ns SRAM cache. If you ran 20ns SRAM cache, in theory you would need to add a cache waitstate to ensure system stability.

In the case of your 40MHz system, you would probably need to use 2 DRAM waitstates so that your memory would operate in spec (75ns - 10ns) = 65ns DRAM required. 60ns is recommended, but many people got by with 70ns just fine. Using 80ns DRAM is clearly overclocking your memory.

A 0ws or 1ws (15ns, 40ns DRAM required) 40MHz 386 is pretty much impossible, unless you are able to construct some of your own SIMMs using modern technology.

I understand what you're saying, and it's right. Don't get me wrong, I'm not trying to get the best out of my machine. For me functionality on such old hardware is much more important than top speed. I was just curious to see if there would be any difference, and I had 6x60ns simms, and also happened to get another 4 very cheap. After all, I conclude that it's a total waste of time to try to do that, and in the end of the day, all my 386 needs, is a matched set of 8x 1mb simms... 😀