You cant use 150nS on a 386, even a sx16 it would be too slow imho. The ram speed is generally set by the cpu clock speed (plus a wait state or two) so you need 80nS or faster like a 486 iirc

Ok that makes sense, thanks. I guess I have no choice but to actually buy SIMMs larger than 256k for my motherboard instead.

My spiraling expenses is getting out of hand!

clownwolf wrote on 2023-07-01, 17:30:

Ok that makes sense, thanks. I guess I have no choice but to actually buy SIMMs larger than 256k for my motherboard instead.

My spiraling expenses is getting out of hand!

Very true. Thanks to the post COVID financial conditions.

Cheers,

Horun wrote on 2023-07-01, 17:09:

You cant use 150nS on a 386, even a sx16 it would be too slow imho. The ram speed is generally set by the cpu clock speed (plus a wait state or two) so you need 80nS or faster like a 486 iirc

The AST Advantage! board is connected to the ISA bus, not to the front side bus. So the RAM speed required on that board depends on the ISA clock. The 6MHz and 8MHz AT systems quoted in the manual run ISA clock at processor clock, so the quote actually means that you need 150ns RAM at 6MHz ISA clock, and 120ns RAM at 8MHz ISA clock. If you can run the ISA clock at processor clock divided by 6 (might also be called CLK2/12), it's at 6.6MHz, which might be slow enough for 150ns RAM to work. If you slowest setting possible on that board is processor clock divided by 5 (CLK2/10), or it uses a dedicated 8MHz or 16MHz crystal as clock source for the ISA clock, 120ns RAM is required.

Nevertheless, you are completely correct that 150ns or 120ns RAM is a bad fit for a 386SX-40, as is every solution that uses the ISA bus to expand memory. This kind of memory expansion got obsolete as early as the ISA clock is lower than the processor clock, i.e. with 12MHz 286 systems. The performance of ISA-based RAM expansions in 386SX-40 systems is awful, yet it might be useful as disk cache in DOS. It is likely no pleasant experience as main memory in Windows 3.1, though.

Having too little memory in Windows 3.1 is worse than having slow memory, I think.
Windows 3.x needs contiguous memory to properly work.

Windows 3.1 on a 10 MHz 286 with a humble 1 MB RAM:

https://www.youtube.com/watch?v=zc2fVXozxwU
https://www.youtube.com/watch?v=URktiHd30Qo

Bus and CPU run at 10 MHz (as selected in CMOS Setup). 1 MB is a joke, of course. 2 or 4 MB or more would allow business use, though.
I had done the upgrade, but a fellow Tower AT owner asked me to keep the original state of the CPU board intact (which I did).
I'll maybe add a dedicated ISA memory board in the future, haven't decided yet.

PS: Back in the 90s, my 12 MHz 286 PC had 70ns SIMMs installed (like common in 386/486 PCs).
100ns 0r 120ns were considered museum's pieces by then. An XT-era legacy.
Anyway, just sayin'.

Edit: I probably shouldn't say anything anymore, but..
The RAM ratings for the card do merely correlate with the AT/USA bus speed, not the CPU speed.
If the ISA slot runs at 6 to 8 MHz, the ancienr 120ns RAMs can still work.

It's simply that the manual is so old. It probably makes the assumption that both CPU and bus speed are the same.

Which used to be in the days of the IBM PC/AT Model 5170 (slow timings!). It came in merely two speeds, 6 and 8 MHz. No higher end version was released afterwards, as far as I know. *Maybe* that's also a contributor as to why ISA specs settled on ~8 MHz finally.

Anyway, these are just my two cents. Even if there were timing issues, wait states could be added for stability.
Though personally, I'd favor slow timings if they'd allow for zero wait state operation.

That being said, performance is highly individual.
I thus recommend to simply try things out yourself and see if performance is good enough. If the bus isn't being overclocked, no harm is done to the card, anyway. 🤷‍♂️

If possible, use the AST as an XMS or EMS card only. That way, merely those programs will access the card who have a real need for further memory.
Little games will use memory below 1 MB and run via fast, chipset controlled memory.

Jo22 wrote on 2023-07-01, 21:21:

Having too little memory in Windows 3.1 is worse than having slow memory, I think.
Windows 3.x needs contiguous memory to properly work.

Yes, fair enough. What I was trying to express: If the OP wants to run Windows 3.1, using an ISA memory board is better than nothing, but using on-board SIMMs will provide a considerably better experience, so it's definitely worth trying to get a some 1MB SIMMs. On the other hand, even the Advantage! might be fast enough to provide a good disk cache solution for DOS.

mkarcher wrote on 2023-07-01, 21:52:

Yes, fair enough. What I was trying to express: If the OP wants to run Windows 3.1, using an ISA memory board is better than nothing, but using on-board SIMMs will provide a considerably better experience, so it's definitely worth trying to get a some 1MB SIMMs. On the other hand, even the Advantage! might be fast enough to provide a good disk cache solution for DOS.

Hi, that makese sense. My father, which was working as a programmer/developer in these days, had used the extra RAM in his AT in a similar fashion.
He used it for creating RAM disks, to work with lots of temporarily files.
Such as files created/needed by a compiler (dbase translator/Clipper, Turbo Pascal, Mix C etc).