Cacheable RAM on Socket 7 platforms

One thing I completely forgot about since I had a Socket 7 system was the whole “Cacheable RAM Size” also called “Cacheable Area” concept.

In short this implied that you could have a motherboard supporting 768MB RAM but only the 256 first MB could be accessed quickly by the CPU and the 512 other MB were slow at the point your system could be slower with 768 MB than 256 MB…so you probably wonder where this limitation comes from and what to chose today to max out the 768 MB you want on your motherboard, right? 😉

First of all you have to remember that in 1998-2000 not that many people even had 256 MB in their systems so this problem didn’t affect many users. But let’s go to the cause of this problem…the “Tag RAM”; it’s a small memory usually located in the chipset which keeps track of where in memory the entries stored in the L2 cache are. So the “Cacheable RAM” one can address is dependent on the Tag RAM size and the chipset design.

For K6 and K6-2 CPUs (not the K6-III and “+” models) the rule to know what RAM size is cacheable is quite “simple”:

 VIA MVP3 with Write Back cache strategy set in BIOS

  • With 512 kB Level 2 Cache, 64 MB are cacheable
  • With 1024 kB Level 2 Cache, 128 MB are cacheable
  • With 2048 kB Level 2 Cache, 256 MB are cacheable

VIA MVP3 with Write Through cache strategy set in BIOS (2-3% slower system)

  • With 512 kB Level 2 Cache, 128 MB are cacheable
  • With 1024 kB Level 2 Cache, 256 MB are cacheable
  • With 2048k B Level 2 Cache, 512 MB are cacheable

ALI Aladdin V revision D and E

  • With 512 kB Level 2 Cache, 128 MB are cacheable
  • With 1024 kB Level 2 Cache, 128 MB are cacheable

ALI Aladdin V revision G

  • With 512 kB Level 2 Cache, 512 MB are cacheable
  • With 1024 kB Level 2 Cache, 4096 MB are cacheable

Just to help you a little bit more, the ALI Aladdin V revision G chips are used by ASUS for the P5A since revision 1.06 and for the P5A-B since revision 1.05. Most of the P5A boards out there are revision 1.04. But how does one actually check for the revision? Well it’s written on the northbridge, it’s the last letter from the line just above “Taiwan”.

ALI Aladdin V

ALI Aladdin V Northbridge – Revision E

Now you are probably thinking you are pretty much screwed as finding an ALI Aladdin V to support your shiny 768 MB RAM isn’t an easy task…well not completely…let me introduce you the K6-2+ and K6-3(+).

With these chips and their onboard L2 cache (256 kB for the K6-III(+) and 128 kB for the K6-2+) all these issues magically disappear and the limit is 4 GB! So just install one of the “+” chips if you can and need RAM…

Now there is another thing to be aware of…due to a hardware design problem, the Asus P5A with the ALI Aladdin V revision G do not support the “+” CPU well at all, in fact they run extremely slow!

So, now you pretty much have all the info needed to maximise your RAM usage!

7 thoughts on “Cacheable RAM on Socket 7 platforms

  1. congratulations for the nice website, its good that you want to preserve the information about this nice old hardware.

    i think i found a mistake, where you talk about the write back strategy on the mvp chipset

    • Hello, what do you think is wrong? It’s the info I found on various websites and I unfortunately don’t have an MVP3 to test it…

  2. Where did you find the info about the P5A with ALI Aladdin V revision G not supporting the “+” CPUs very well? I’d like to read more on this.

  3. I just bought an Asus P5A with a k6-II 500 AFX and 384mb of RAM, before reading your article, for about $15.00.
    For my surprise, it is a revision G Alladin, it made my day :).
    Great site you’ve got here!

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