Sets of 4, all same size.

On 16-bit boards (286 and earlier) can be used in pairs.

Thank you. If I've got 4x 1MB, 70ns, can I add 4x some-other-size and speed? So if I add 4x 4MB, 60ns, that would give me a total of 20MB, and I'm assuming all 8 SIMMs would run at the slower (70ns) speed?

Yes, should work.

Unfortunately 4MB 30-pin SIMMs have been obscenely expensive recently.

Yeah, just asking theoretically, so I can understand how it works. If anything, I'll probably either upgrade to 4x1MB 70ns for a total of 8MB, or if the price is right, 8x1MB 60ns so I can experiment with RAM speeds and benchmark the differences.

someone on this forum has already tested on a frankenstein mainboard - multiple 72pin simms were faster than 1 dimm;
i guess it might depend on the cpus bus width?
or maybe the amount of memory banks is a factor itself?

60ns can be run with faster bus. Otherwise there are no benefits.

Once I overclocked a 486slc-33 to 40MHz and it wasn't stable. I thought the chip can't take it. After a while I tested it with 60ns memory and it worked perfectly. On majority boards you won't get any benefits as 70ns is fast enough. But it's good to have some faster for testing,

You should be fine with mixed speeds and with my boards I am not having any issues at 40mhz, there are some 4mb and 16mb sticks but they are not cheap. Might be able to get a 64mb kit for around $50 but sadly 16mb kit (4x4mb) isn't much cheaper unless you get lucky on a bid.

> 8MB is usually not worth it on 386s / 486s. Virtually no software will use it. Especially not games from that era.

noone ever did homemade modules of this kind? i mean the chips got faster with time and could, if of similar type, be used to populate old type modules to get ultra fast memory; or is the newer memory always done from chip of incompatible technology?

I was under the impression that with faster RAM, you could be more aggressive with your memory settings in the BIOS:

So, the DRAM Speed Option, Write CAS Pulse, Write Cycle, etc.

mrau wrote:

noone ever did homemade modules of this kind? i mean the chips got faster with time and could, if of similar type, be used to populate old type modules to get ultra fast memory; or is the newer memory always done from chip of incompatible technology?

DRAM < EDO < SDRAM < DDR < ...
Incompatible technologies.

FPM preceded EDO. They're all types of DRAM.

FPM chips were made as low as 50ns and even 45ns, but SIMM's under 60ns are very rare. 50ns is a lot more common in EDO SIMM's, but those came out in the latter half of the 90's and they're incompatible with many older memory controllers. 486 mobo's also don't usually give options to take advantage of fast memory, unless you're really cranking up the bus.

PC's used 3/9 chip SIMMs (parity) while old Macs can use 2/8 chip SIMMs and the 3/9.

I have a box full of Mac memory and most of my PC stuff is in systems.

70ns pretty much is good enough for any system.

I Think it would possible to fit SRAM on SIMM Modules and make a custom PCB.
But SRAM is also expensive.

2x 16 MB SIMMs are useful for AWE32. Gives 28MB of usable soundfont memory.
Also, it is possible to solder a single 72-pin module instead of 4 30-pin SIMM modules. But most 72-pin SIMM don't have parity, which is required by most 30-pin SIMM motherboards. This is the error I made in 90s when actually attempting to do this. The RAM was there but failed the parity check immediately.

A parity calculator such as 74F280 may be able to fake it. Needs some support logic though.

SRAM may be even more expensive at those capacities and needs support logic, voltage regulator etc.
There's als Pseudo SRAM like http://www.mouser.de/new/issi/issi-pseudo-sram/ - BGA and multilayer PCBs anyone? 😁 Also not that much faster.

For an AWE32 you can also use half a 64MB DRAM stick xD.

IIRC, AWE32 doesn't even need parity!