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Thread: L2 Cache questions

  1. #1

    Default L2 Cache questions

    Hi all,
    I've got a 486 motherboard with a 486DX4-100 CPU. Its runs an AMI bios and I've enabled internal cache and also L2 cache mode as Wr-back, Internal Cache L1 Wr-Thu and is not changeable. On the AMI-BIOS System config screen I see 256kb cache memory.

    When I run cachechk it says: "Machine seems to only have one cache. [read]" I only see the 8k cache which I guess is the L1 cache in the actual CPU??

    Its a newer board as it has both PCI and ISA slots. The cache is embedded on the board. Is there any other diagnostic software I can test if my cache is good?

    Cheers,
    Not all those who wander are lost. - J. R. R. Tolkien

  2. #2
    Join Date
    Jan 2014
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    Western North Carolina, USA
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    There were many 486 boards with fake cache; a good reference can be found at http://www.redhill.net.au/b/b-bad.html EDIT: Also you may find https://www.vogons.org/viewtopic.php?t=36719 to be interesting. I personally have at least one fake cache board here somewhere.... none of the traces that connect to the cache chips (labeled "write back" which can be a red flag, since the cache RAM itself is not what makes it "write back") connect to anything else on the board.....

    The diag you've already run is quite likely telling you it's a fake cache board.
    Last edited by lowen; March 4th, 2020 at 04:03 AM.
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  3. #3

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    Quote Originally Posted by robbo007 View Post
    Hi all,
    I've got a 486 motherboard with a 486DX4-100 CPU. Its runs an AMI bios and I've enabled internal cache and also L2 cache mode as Wr-back, Internal Cache L1 Wr-Thu and is not changeable. On the AMI-BIOS System config screen I see 256kb cache memory.

    When I run cachechk it says: "Machine seems to only have one cache. [read]" I only see the 8k cache which I guess is the L1 cache in the actual CPU??

    Its a newer board as it has both PCI and ISA slots. The cache is embedded on the board. Is there any other diagnostic software I can test if my cache is good?

    Cheers,
    Only the 486s with 16kb internal cache support WB, that's why yours is locked to W-Thru for L1

    Some (few) motherboards can only run L1 and L2 the same way, but probably this is not the case since you have separate settings.
    You haven't posted any pictures from your BIOS options but the first thing I'd do would be to check if in W-thru mode L2 gets recognized. If so, search for a BIOS setting about tag ram and change it from to 8bit, which is for w-Thru, to 7-bit.

  4. #4

    Default

    Here are the screenshots of the bios:
    https://ibb.co/QvbB3dy
    https://ibb.co/6P5X0RY

    I've tried with cache set to WriteThru and the same. I think my board is one of those fake cache boards. Doh!! How much speed increase on a 486DX4-100 will I get with 256kb cache ? The good think about this board is its got PCI slots too. So I can free up ISA slots for all my ISA cards.
    Not all those who wander are lost. - J. R. R. Tolkien

  5. #5
    Join Date
    Apr 2015
    Location
    Austin, Texas
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    2,057

    Default

    If we had a picture of the board, we'd be able to tell immediately if the cache chips were fake or not.

    Motherboard cache isn't terribly useful because it runs on the FSB and has to fight with other bus devices for bandwidth. The only application where it really makes a difference is if you have a large amount of RAM installed, it can cache the memory and make the system a lot faster. This wasn't a big problem back in the day because memory was so expensive that most people didn't have enough for it to be a problem. It really only becomes an issue if you have more than 64 MB.

    I've done cache experiments with a Pentium 200 using COAST modules, and even with 512kb of motherboard cache, the performance difference was at most 10%.

  6. #6

    Default

    Here is a picture of the cache. Its in a hard position to take photos due to where my PC is.

    https://ibb.co/cwJzGmm

    On the board there are two bigger chips that have a sticker on each saying WrtiteBack Chip. I can`t get my phone into it to get a decent picture without pulling everything apart.

    https://ibb.co/WgwjkG5

    But as you mention. it will make little difference in performance so I guess I'll just stick with it. But very interesting to know there were actual cache scams like that going on.

    Cheers,
    Not all those who wander are lost. - J. R. R. Tolkien

  7. #7

    Default

    Here is a picture of the cache. Its in a hard position to take photos due to where my PC is.

    https://ibb.co/cwJzGmm

    On the board there are two bigger chips that have a sticker on each saying WrtiteBack Chip. I can`t get my phone into it to get a decent picture without pulling everything apart.

    https://ibb.co/WgwjkG5

    But as you mention. it will make little difference in performance so I guess I'll just stick with it. But very interesting to know there were actual cache scams like that going on.

    Cheers,
    Not all those who wander are lost. - J. R. R. Tolkien

  8. #8
    Join Date
    Apr 2015
    Location
    Austin, Texas
    Posts
    2,057

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    The "TE11256-20K" DIP ICs are SRAM cache chips. I'm not able to find any datasheets on them, but there are a few places where you can still buy old stock of them, so they're probably real. Whether they're actually connected to anything is another issue, the traces under them look rather odd.

    There also appears to be another row of what looks like may be more memory chips behind those buried under the cables. Those look a bit suspect, like they're not plugged into the sockets correctly.

    As for the "Write Back" sticker, that's the chipset, not any sort of RAM. If you peel the sticker off, you'll be able to see what chipset was used on that board.

  9. #9

    Default

    I'm going to strip this board down in the coming weeks to see it more in detail so I'll post photos. Thanks for all the help so far.
    Not all those who wander are lost. - J. R. R. Tolkien

  10. #10

    Default

    Right. rebuilt my 486 with an Intel 486DX2-66. I loose some speed but resolved all problems. Ultima Underworld II with the patch now works fine. No corrupt video pallets anymore. Strange as cachechk still reports only L1 cache and this board has external cache enabled in the bios and on board they are real IC's not like the other motherboard where they were soldered onto the board. These are removable and look real.

    Maybe cachechk has problems?
    Not all those who wander are lost. - J. R. R. Tolkien

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