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0xCats wrote on 2022-01-05, 12:54:

And there are also these older 72pin SRAM simms made by Dallas (1MB) Using modern 16/32 or even 36bit SRAM (for ECC) chips there […]
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And there are also these older 72pin SRAM simms made by Dallas (1MB)
Using modern 16/32 or even 36bit SRAM (for ECC) chips there would be very little issue in designing an SRAM based memory module.

Advantages of that would mean very low access latencies (good for overclocking) and the option to use very low timings and with some BIOS+chipset mods skipping ram refresh entirely. Since SRAM doesn't require that.

The big factor is how many MB you want it to be and how much you want to spend 😜

64 mb.

Wonder if we could talk jan into adding a sram option to my tyan bios..🤔

Does this mean that we might be able to exceed sd ram speeds using simms?

Mmmm SRAM t2p4...

Not to burst yer bubble but SRA M can’t be just put on a simm (unless your memory controller supported it) dram runs in columns, sram is directly addressed with no refresh.

I know folks who used sram on both a PC JR and on an IBM AT

From what I can tell they removed as much dram as possible and installed sram to an isa card

I have often wondered how folks back in the day claimed they were able to remove all dram and use just sram in IBM Compatibles, boards I’ve tested throw a post error with sram in the isa slot but no dram on board.

Historically using just sram gave your old Pc a fair boost by removing the overhead of refreshing dram, never saw a how to made but have seen claims of people doing it many times.

rmay635703 wrote on 2022-01-05, 18:27:

Not to burst yer bubble but SRA M can’t be just put on a simm (unless your memory controller supported it) dram runs in columns, sram is directly addressed with no refresh.

I figure that if you put some glue logic, most prominently a row address latch, on the SRAM SIMM, you can make it look like DRAM to the controller. A 15ns fast CMOS SRAM and some 74ACT series logic is likely still faster than your average 60ns DRAM. But you are definitely right that you can't just wire SRAM chips to the SIMM pins, as you can do it with DRAM chips. And a SRAM SIMM emulating DRAM only improves performance if the mainboard allows you to make memory access timing faster than the DRAM chips you have can handle.

So: If you want to run a 486 board at DRAM timings designed for FSB25 at FSB50, you could have a lot of fun with DRAM-emulating SRAM SIMMs. If you want to avoid memory addressing wait states on your XT-class machine, it's not going to help, except for a small performance gain obtained from disabling refresh.

By the way: The opposite way also exists as a product. Chips that internally contain fast a fast DRAM and a built-in memory controller, so they can be accessed just like a slow SRAM (think of 100ns SRAM, not 10ns SRAM). For high-capacity, low performance chips, this is the most cost-effective way to implement something that behaves like an SRAM today.

It’s unfortunate many 486 and early Pentiums had meh memory controllers that could not be set to a true 0ws, an emulated dram coupled with better timings would give a definite boost especially to the old p60’s

My conundrum was how to add sram directly to the cpu bus, I have several systems that are crippled to small amounts of addressable extended memory by design

If I could wire up a 4mb cache board directly to a socketed cpu like my Tandy 1000rlx I could expand the ram beyond the 384kb extended it allows, ditto one of my 386sx systems that can’t expand beyond 5mb (but I only have 1mb and no proprietary expansion)

Ah well

rmay635703 wrote on 2022-01-05, 19:51:

It’s unfortunate many 486 and early Pentiums had meh memory controllers that could not be set to a true 0ws, an emulated dram coupled with better timings would give a definite boost especially to the old p60’s

You can get quite fast EDO RAMs till today. There are 35ns 40-pin TSSOP 16-bit EDO RAM chips that you can use as drop-in-replacement on PS/2 SIMMs. The only downside (making it impractical) is the low capacity of those chips. They are 256k x 16, so you can use them to build 1MB "single-sided" or 2MB "double-sided" SIMMs. This will result in not enough RAM for typical Pentium-era software, though.