Ideas:
1. Run a memory test program like memtest86+
2. Reset BIOS settings to default/safe values, in case there are memory timing options that the new SIMMS can't withstand
3. Completely disable motherboard cache from BIOS, as a test of course
4. I'd say test the SIMMS on another motherboard but I suppose if you had one you'd have done it already

I couldn't get memtest to work, probably because of the new RAM sticks. Haven't tried with my old ones. I reset the BIOS, as well as tried fooling with different settings for RAM in the BIOS, but it really only allows me to select either 60ns or 70ns with the rest being autofilled. I can do a 'manual' setting, but there's some hi tech wizardry going on in those settings that I'm not familiar with.

However when I disable external/internal cache it boots up, but is very slow. When I have both internal and external cache enabled, it restarts. My old RAM works perfectly with all cache enabled. My new RAM won't boot with internal and external cache enabled, only internal enabled, and is slow.

EDIT: I can get memtest to work with the external cache disabled too. The RAM passed.

Which memtest are you using and how does it fail? It doesn't sound like you're booting into Memtest86+...

A full test run takes >8h. If RAM (or cache) is bad you can sometimes find out almost immediately, but to be sure a setup is good you need to run for at least 8h (leaving it on overnight works best in my experience), so after 1h you can't say anything "works perfectly", let alone if you've been doing other things as well.

However this sounds like a caching issue, more specifically with L2 cache. The system being slow with cache disabled is expected: that shows you why the cache is there in the first place.

But... to be sure it's not something else it would help if you give specs of the SIMMs, in particular the model# of the chips on both the ones everything works well with and on the other one. Have you been testing with only the new SIMMs in the system, or with both new and old? In the latter case this might also be a compatibility issue between SIMMs.

No need to mess with internal cache, just the external/L2. Now I don't know your configuration, but I'd make sure the jumpers for the cache (if any) are set correctly and if the configuration allows it, remove 1 bank (make the cache half the current size) and try again, then switch the chips in an attempt to identify faulty cache chips. If your BIOS has write-through (WT) and write-back (WB) options for the cache also try the other option.

dionb wrote on 2024-08-06, 07:37:

A full test run takes >8h. If RAM (or cache) is bad you can sometimes find out almost immediately, but to be sure a setup is good you need to run for at least 8h (leaving it on overnight works best in my experience), so after 1h you can't say anything "works perfectly", let alone if you've been doing other things as well.

Totally agree, but in my experience when the problem is not some weird crashes but so obvious that windows don't even load, memtest usually reports problems within the very first cycle

Could it be a question if EDO vs FPM memory? And as such, BIOS settings?

I'm using memtest86 4.10 from a floppy. It works fine when I disable external cache, just like with Windows. The number at the top by 'Pass' went to 100% so I thought that was all it took, but now I see I've got to run it for a long while.

I've tried the new and old ones. The old ones work fine with everything. Two sets of new ones, both with different specs, gave me the aforementioned issue. I actually posted a thread a couple weeks ago pinpointing the RAM I needed, located here: SIMM and DIMM slot RAM

The old RAM is 72-pin SIMM 70ns 2Mx32 located here: https://www.tiger-technik.de/en/Arbeitsspeich … r385::5625.html . The new RAM is 72-pin 60ns 4Mx32. located here https://www.ebay.com/itm/141125444372 - I think both are EDO, but the old ones are possibly FPM since I'm seeing ambiguous listings.

My motherboard manual says it accepts both FPM and EDO RAM fine. The only thing that changed was the speed, but my board supports both 70ns and 60ns.

H3nrik V! wrote on 2024-08-06, 07:50:

Could it be a question if EDO vs FPM memory? And as such, BIOS settings?

I just googled the actual number on the chips themselves of the old RAM and contrary to the listing above, this says it's actually FPM: https://www.datasheets360.com/part/detail/km4 … 80790554134072/

So now the common denominator seems to be that FPM/70ns is working and EDO/60ns isn't. According to my manual https://dosdays.co.uk/media/aopen/aopen_mb_AP5VM.pdf I should be fine with either, and the board supposedly autodetects the type of RAM, so no need for jumpers. The one thing I noticed is that a DIMM needs a jumper for EDO or SDRAM, but that's for a DIMM stick. I'm using SIMMs. Hmm.

Syntho wrote on 2024-08-06, 08:13:

H3nrik V! wrote on 2024-08-06, 07:50:

Could it be a question if EDO vs FPM memory? And as such, BIOS settings?

I just googled the actual number on the chips themselves of the old RAM and contrary to the listing above, this says it's actually FPM: https://www.datasheets360.com/part/detail/km4 … 80790554134072/

So now the common denominator seems to be that FPM/70ns is working and EDO/60ns isn't. According to my manual https://dosdays.co.uk/media/aopen/aopen_mb_AP5VM.pdf I should be fine with either, and the board supposedly autodetects the type of RAM, so no need for jumpers. The one thing I noticed is that a DIMM needs a jumper for EDO or SDRAM, but that's for a DIMM stick. I'm using SIMMs. Hmm.

Have you been testing with only the new SIMMs in the system, or with both new and old?

dionb wrote on 2024-08-06, 08:17:

Have you been testing with only the new SIMMs in the system, or with both new and old?

Oh wait, sorry. I thought you meant something else No, I haven't. I've kept them separate. I have two sticks of old, two sticks of new, and I never combine new/old together at the same time.

Syntho wrote on 2024-08-06, 08:19:

dionb wrote on 2024-08-06, 08:17:

Have you been testing with only the new SIMMs in the system, or with both new and old?

Oh wait, sorry. I thought you meant something else No, I haven't. I've kept them separate. I have two sticks of old, two sticks of new, and I never combine new/old together at the same time.

Ah, then it's not an incompatibility issue between SIMMs. If the one is FP and the other EDO, they wouldn't work together, but that's not the problem if you're testing them separately.

Did you recently buy the "EDO" modules that turned out to be FP? After some discussions about 30p "EDO" SIMMs it turns out there are some big sellers on eBay who don't understand the difference and are selling everything in SIMM form factor as "EDO" even if it's FP, which confuses the situation hugely.

But either way both should work - a VX chipset board should be able to use just about any 5V 72p SIMMs with cache enabled. Have you tried resetting BIOS to defaults? If it's on'auto' already that shouldn't make much difference, but it's worth a try.

Btw you can manually set DRAM timings (those greyed out bits) by going to the DRAM Timing setting and changing it from "60ns" or "70ns" to "Manual". Not that I expect the subtimings to change anything here - if they were the problem you'd not see any difference in behaviour with caches disabled.

Finally, looking at that "EDO/SDRAM" selector for the DIMM, that's a - dangerously - mislabeled option. It's a voltage selector where "EDO" is 5V and "SDRAM" is 3.3V. Now SDR-SDRAM DIMMs are always 3.3V, but EDO DIMMs are available in both voltages and the keying of the 168p slot is for 3.3V DIMMs, so if you set it to "EDO" and put in an EDO DIMM that actually fits, you might well see the magic smoke being released. However that's not relevant here - you're only using SIMMs and they only work on 5V (well, there *are* 3.3V SIMMs which may or may not be 5V tolerant, but the chips you posted the datasheet for are definitely 5V units and 3.3V SIMMs are very rare and usually have far larger capacity than the stuff here).

The SIMM supported by this mainboard can be identified by 4 kinds of factors,
Intel VX chipset does not support 64M bit technology.
♦ Size: single side, 1Mx32 (4MB), 4Mx32 (16MB), and double side, 1Mx32x2
(8MB), 4Mx32x2 (32MB).

I just ordered some more FPM RAM. I don't know why the system isn't taking any EDO RAM I put into it. I'll update the thread when I get the new stuff and see if it works.

The EDO RAM I tried is 4Mx32 and 4Mx32x2, in pairs. Neither set worked. My FPM works flawlessly though. I wonder what's going on...

There's something fishy going on here. I just got a new set of FPM RAM and the same thing is happening. I booted Windows 95 with the full amount (64mb) and it froze. I took out two sticks back down to 32mb, and this time Windows restarted like I posted above. So EDO vs FPM RAM isn't the problem.

Basically, this system doesn't seem to like something with more than 16mb or so of RAM in it. The only sticks that do work are 8mb ones. The ones I just got are 16mb a piece. I tried starting Windows in Safe Mode but it says 'Himem is testing extended memory' and it never goes past that.

I guess the only hint here is cache because when I disable it it boots fine with both new sets of RAM. I don't know why the cache would work fine with my old 16mb set (2x8mb) and not anything higher. The L2 cache appears to be onboard.

Are you sure the FPM really is FPM? Not that that is likely to be the issue...

As you describe the issue, it almost sounds like a specific memory location in the tag RAM the chipset uses to keep track of which memory locations are cached is faulty. If the board had been a bit older, with separate DIP SRAM cache and tag chips that would have been easy to troubleshoot and fix (find offending chip, replace it). But this board is - just - new enough to have everything soldered. The tag RAM is the SOJ-28 chip between the DIMM slots and the upper 82438VX cache controller.

If you're very confident with desoldering large SMD components you could desolder it to test it. But failing that, it could be as simple as one of the legs being bent, damaged or simply not making good contact with its pad. Take a look there, and in case of doubt, make the best photograph of that chip and its legs from the side you can and post it here.

It's definitely FPM. My POST results say if it's EDO or FPM RAM since my board auto-detects the type.

I think I've located the chip you mentioned. It doesn't look bad to the naked eye, but I don't think getting in there and unsoldering it would be worth it. While I don't know how how all of that stuff works under the hood, I'd think that the system wouldn't work at all or at least give me trouble if something weren't soldered right with the old RAM in there. But it's worked fine for 3 years now.

DOS works fine. It's Windows that doesn't work, both 95 and a 98SE installation. So maybe some sort of weird Windows setting is conflicting with the new RAM, and a reinstallation will fix it. Ridiculous, but maybe worth a try to install a new copy of 95/98SE...

The manual had a large section on ram use iirc. And about what size can be used in which banks. You read all that and made sure you stick to it?

ux-3 wrote on 2024-08-13, 10:39:

The manual had a large section on ram use iirc. And about what size can be used in which banks. You read all that and made sure you stick to it?

Absolutely. The system wouldn't boot at all if something were 'wrong' with the RAM.

Alright, I tried reinstalling Windows. Doesn't work. Something is very weird about this whole thing and I don't know if it's worth it to keep debugging it. 16mb of RAM works. 32mb or more doesn't.

When I have 32mb in there, Windows restarts immediately. With 64mb, it freezes.
For reinstallaing, 64mb freezes the installation, but 32mb gives me:

A Fatal Exception 06 Has Occurred at 0B33:00000092. The current application will be terminated

The only other thing I can think of is that my original 8mb sticks are period correct. The other RAM is newer stuff from Ebay. Maybe some sort of spec changed and the way they manufactured the RAM changed over time and my motherboard just plain doesn't like newer stuff. I'd have to track down some older RAM, but I really don't want to keep buying stuff over and over. I'm out of ideas other than that.

Syntho wrote on 2024-08-13, 15:01:

Alright, I tried reinstalling Windows. Doesn't work. Something is very weird about this whole thing and I don't know if it's wor […]
Show full quote

Alright, I tried reinstalling Windows. Doesn't work. Something is very weird about this whole thing and I don't know if it's worth it to keep debugging it. 16mb of RAM works. 32mb or more doesn't.

When I have 32mb in there, Windows restarts immediately. With 64mb, it freezes.
For reinstallaing, 64mb freezes the installation, but 32mb gives me:

A Fatal Exception 06 Has Occurred at 0B33:00000092. The current application will be terminated

The only other thing I can think of is that my original 8mb sticks are period correct. The other RAM is newer stuff from Ebay. Maybe some sort of spec changed and the way they manufactured the RAM changed over time and my motherboard just plain doesn't like newer stuff. I'd have to track down some older RAM, but I really don't want to keep buying stuff over and over. I'm out of ideas other than that.

dont use EDO ram, i had nothing but problems with mine also two 8mb sticks, sometimes i wouldnt get any video out and when i did installing windows was impossible it wasnt reliable, and prob because the onboard video was using 4mb of it, also dont use two different types of ram at once, according to the manual for my board (socket 7) it can cause damage, which didnt occur to me.

you mentioned changing/resetting the bios then having problems, three options to look out for are "memory hole at 15-16M", "shadow video bios" or cache bios/video bios" disable all of them, the memory hole one if i remember will prevent windows from booting so expect to do a fresh install.