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386 cache write back chip

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    #1

    386 cache write back chip

    Hi
    I have a M321 V2.5 which has a socket for a write back chip. What chip can go in there, its a DIP-12 socket.
    The cache is currently W24257AK-15 x 8.

    Thanks
    Andy
    Tags: None
    #2
    It takes a 16kx4 chip, in DIP-22 form... you align pin 1 and leave the last two positions in the socket empty. That's a DIP-24 socket, BTW, not DIP-12.

    Common part numbers to look for are: CY7C164, QS8888, and IDT 7188, but there are a bunch of others as well. Make sure you pay attention to the speed grade. Ideally you'd want 15ns to match the rest of your cache, but 20ns would probably be fine... trouble is, ones faster than 25ns can be tough to find.

    Comment

      #3
      http://stason.org/TULARC/pc/motherbo...l#.UirElcZ8J00

      Comment

        #4
        Thank you for posting that website! I was able to use it to find a motherboard similar to mine

        Comment

          #5
          I have the same mobo. I use one CY7C166-15PC in 24-pin DIP package (as pictured). Speedsys 4.78 reported that the memory bandwidth got almost doubled from 26MB/s to 54MB/s. The real performance boost is less significant though.

          However, if you are attempting to get W24257AK-15 x 8 to work as 256k cache, the write-back chip (U32) is not the key but the TAG chip at U17 has to be the 9th same W24257AK-15 if it is not yet so. M321 motherboards are available in many different versions from v2.1 to v3.1. Most of M321 (>= v2.5) have the tag chip (U17) permanently soldered on board, as well as the jumpers at J5 ~ J9 are removed by soldered wires. This gives considerable trouble in upgrading the cache from the original 128k to 256k. You could be very lucky if your M321 v2.5 comes with a socket at U17 and jumpers at J5~J9. I saw only one sold on eBay for $87 a year ago.


          M321_WB.jpg
          Last edited by Dca2; September 7, 2013, 04:12 PM.

          Comment

            #6
            So if i replace the soldered on U17 with a socket i could use all the cache installed? The jumpers are still in place. But if i change them to that on the staton site for 256k, it fails boot.
            Andy

            Comment

              #7
              Yeah, that was my case. I carefully desoldered the original AS7C164-20 and replaced it with a DIP-24 socket, put in an UM61m256k-15, I got 256k cache working before I plugged in the write-back chip.

              Comment

                #8
                I have replaced U17 with a DIP-24 socket and installed a UM61256K-15 (all i have). I will fire it up tomorrow. No U32 installed yet.
                Andy

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                  #9
                  Darn it. Failed boot on 256k and 128k cache settings.
                  Andy

                  Comment

                    #10
                    Hopefully you meat DIP-28 socket instead of DIP-24 socket (sorry for my typo), or otherwise your UM61256K-15 won't fit physically.

                    A good start of diagnostics is to test all the 9 cache chips on another motherboard, ideally a 486 board. Otherwise, you could try to boot with turbo mode off (put a cap on J12), or even without cache (disable "External Cache Memory" in BIOS).

                    According to my experience, 256k cache works regardless of U32.

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                      #11
                      I think i damaged something getting the original U17 off and sockets on. Even with a new 61c64 in U17 & the original 4 chips the cache fails on boot.
                      Andy

                      Comment

                        #12
                        Sad to read this result - assuming that you've already done all general diagnostics such as: checking all jumpers including J3, reseting CMOS and loading Power-On Default...etc. Since your motherboard passed POST without error. It's still hard to conclude a sever hardware damage.

                        Comment

                          #13
                          I have a "Compass" 386 motherboard that also has the "writeback chip" socket. The problem is, when I install the 16kx4 SRAM in the socket I can't detect any difference in performance. I am using speedsys graphs to measure memory throughput.
                          I've seen other 386 motherboards that have a writeback/writethrough option in the BIOS setup, but mine doesn't appear to have this option. It is possible there is a jumper needed to enable writeback mode?



                          http://www.uncreativelabs.de/th99/m/U-Z/32792.htm
                          Last edited by Anonymous Coward; October 13, 2013, 05:37 AM.
                          "Will the Highways on the internets become more few?"

                          V'Ger XT

                          Comment

                            #14
                            Check the underside of the motherboard. Are there traces from the cache to the CPU? I don't see any on the side that is pictured. Many of the fake cache sockets didn't interact with any other part of the motherboard. No connections means it won't work.

                            Comment

                              #15
                              I believe that this is motherboard dependent. My M321 mobo does not have any jumper(s) for enabling/disabling write-back mode on cache. There is also no BIOS option to do this. Just throw in a correct chip, the BIOS will automatically pick it up and ALWAY use it. The strange thing is that Speedsys reported that the memory bandwidth was almost doubled, but the write speed curve (in blue) was still a flat line, as if the cache was not involved at all.

                              I have another 386 mobo, it does not need an additional chip for write-back mode but offers a convenient BIOS option for switching between WT & WB.

                              Originally posted by Anonymous Coward View Post
                              http://www.uncreativelabs.de/th99/m/U-Z/32792.htm
                              By the way, it seems that the document in the th99 link does not mention the "write-back socket" or I just missed something?

                              Comment

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