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Deskmaster 486 Cache...

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Reply 20 of 27, by WazMeister

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Ydee wrote on 2021-03-20, 08:43:

Unfortunately, this may not be true - there may be 4 modules of 4 MB on the board, of which BIOS can only see half, i.e. 4x2 MB, which gives the 8 MB of visible RAM. SIMM memory modules with a capacity of 2 MB were not produced, if I can remember.

So if it has onboard how can I tell, take the simms out and see what is reported?
The board can take upto 32mb according to manual.

So though pc says 8mb it's possibly not really 8mb? Or possible 4mb on board and them 4 simms are 1mb? Hence 8mb? So my ideal upgrade be 4x simms of 4mb for it all to work? For the spare 4x slots?

Reply 21 of 27, by Ydee

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As indicated in the manual, the computer has the option of upgrading to 36MB memory using 4MB modules. I.e. if there are 8 slots of 4MB, then there must be 4MB on the board. Your other 4 slots are busy, so probably 4x1MB modules. The modules have 9 chips, i.e. a parity SIMM. If you use another 4 modules of 4MB, you will have a total of 24MB of RAM - if 4 of 1MB, then 12MB.

Reply 22 of 27, by mkarcher

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WazMeister wrote on 2021-03-28, 08:59:

It has 8mb ram.
That's what's reported by system. So are we saying that it's more than 8mb or less?

If the memory works good enough to not have windows 3.1 crash on the first start, you definitely have at least 8MB installed. It is very unlikely that the SIMM modules in your board are in fact 2MB SIMMs, because then the nine chips would have to be 2M x 1 chips each, which were never a common mass-produced chip type. This leads to the conclusion that most likely, the SIMMs actually should make up for 16MB, but at least one of the modules is broken in a way that the memory size detection of the BIOS is fooled to just detect 8MB. If there were 2MB SIMM modules, they would use exactly the same amount of traces to connect to the chipset as 4MB modules use, so a broken trace or socket on the mainboard is very unlikely to cause the misdetection of a 16MB bank as eight megabytes.

To remove the last doubt whether you indeed have 4 modules of 4MB each, you can take a look at the model number of the chips on the module. I expect to find 9 chips of 4M x 1 each. Typical model numbers of these chips include HYB514100, HM514100 and M5M44100.

Reply 23 of 27, by WazMeister

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Oh boy, sorry I'm so confused. What's all this 9 chip and 2x1 and 4x1 talk mean?

Does old ram work differently I. E. The chips it has on stick is ram and type?I just want to know how to understand the ram, what it is and what I needed to get to add more

Reply 24 of 27, by Ydee

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BIOS reports 8 MB of memory, right? The manual states, that you can upgrade memory up to 36 MB using 8 slots and 4 MB modules. This means, that 4 MB of memory should be soldered on board as a basic configuration with empty SIMM slots. So if you have 4 MB on the board and the system reports 8 MB with 4 slots filled, there are probably 4x1 MB modules in the slots.

Reply 25 of 27, by Doornkaat

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Ydee wrote on 2021-04-07, 07:48:

BIOS reports 8 MB of memory, right? The manual states, that you can upgrade memory up to 36 MB using 8 slots and 4 MB modules. This means, that 4 MB of memory should be soldered on board as a basic configuration with empty SIMM slots. So if you have 4 MB on the board and the system reports 8 MB with 4 slots filled, there are probably 4x1 MB modules in the slots.

Ydee wrote on 2021-03-28, 10:38:

As indicated in the manual, the computer has the option of upgrading to 36MB memory using 4MB modules. I.e. if there are 8 slots of 4MB, then there must be 4MB on the board. Your other 4 slots are busy, so probably 4x1MB modules. The modules have 9 chips, i.e. a parity SIMM. If you use another 4 modules of 4MB, you will have a total of 24MB of RAM - if 4 of 1MB, then 12MB.

You're spot on! The RAM is even visible in the photos.

The Mystery Of The Second 4MB.jpg
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And in the service manual you can see it is connected to the main RAM slots and not part of the VRAM (that's underneath the HDD in the ebay picture).

The Mystery Of The Second 4MB pt.2.jpg
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The manual also tells me the chips' locations are U65-U68 and U71-U74. Looking them up in the Main Board Parts List they are listed as "IC-DRAM : 44C1000A ,1M*4".
Eight chips of 4mb each. This perfectly fits the mysterious 4MB.
Everything is fine with the RAM, there are no 2MB modules and likely no 4MB modules either. No modules have been removed after the seller took pics, nothing is broken or bugged and only showing as 8MB. There's actually 8MB of RAM installed. Case closed. 😉

BTW, OP: Instances like this are why the document is not the "worse manual ever" but actually a really helpful tool. You just tried to read it as a user's manual, while it's really a service manual. It is not intended to help the end user set up his computer, it is meant to help a service technician or advanced user to understand and troubleshoot this machine. You even get schematics and a complete component list. If a resistor or capacitor on the board fails and you can't read the markings just look it up. No guessing needed.
All this in depth information is overwhelming to a novice so no wonder it is confusing to you. Still there is really no reason to damn it. I wish a service manual was still included with most complex electronic devices because it really aids in repairing your stuff.
Actually if we had something like this for a later Socket 3 board it would be really easy to just make a clone.

Reply 27 of 27, by Ydee

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Doornkaat is an expert, I know very little about such old PCs. If I remember correct, you can't only fit 2 SIMM slots, but either all 4 or nothing. For 32-bit CPUs (of which 486 are) the memory bank consists of 4 slots and the memory bank must always be fully occupied in order to function. So you have to get four more SIMM modules.