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Thread: Max. cacheable RAM - M571 / SiS 5597

  1. #1

    Lightbulb Max. cacheable RAM - M571 / SiS 5597

    Hello fellows,

    First, this is my setup:

    PcChips M571 with the SiS 5597 chipset (as reported by speedsys)
    CPU is Pentium 233 MMX @291 MHz (83x3.5, 2.9v)
    I can use either 64, 128 or 256 MB of RAM memory

    According to this website the Maximum Cacheable DRAM Area is 128MB

    According to a little program called "CTCM", Version 1.7A, by Andreas Stiller:
    Cacheable Area L2 : 128 MByte, Cache Area < Main memory!!

    How can I test how much ram it is actually able to cache?
    What software should I use to accomplish this task in MS-DOS or Win9x?
    What are the implications of using 256 instead of 128 MB if it turns out only 128 MB is cacheable? Is there a way around it? Could I select which part of the RAM I use for software and use the rest, the non-cacheable part as a ram disk, for instance?

  2. #2

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    The datasheet for the chip set states "Support Cacheable DRAM Sizes up to 128 MBytes". Do you have the full 512KB cache?

    As for testing, you should get similar performance with 128MB or 256MB if you stay below 128MB RAM usage. I don't know of a specific program that would allow you to test if the RAM is cacheable. But if the datasheet and other sources state 128MB max, that's likely the max. What are you trying to run on such a system? If you actually need more that 128MB RAM, non-cached RAM is going to be faster than paging to the HDD. If it is very important you could benchmark the system with 128 and 256MB.
    Looking for: OMTI SMS Scientific Micro Systems 8610 or 8627 ESDI ISA drive controller, May also be branded Core HC, Please PM me if you want to part with one.

  3. #3

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    Quote Originally Posted by mR_Slug View Post
    Do you have the full 512KB cache?
    Yes, the L2 cache reported by speedsys is 512 KB
    Quote Originally Posted by mR_Slug View Post
    If it is very important you could benchmark the system with 128 and 256MB.
    Quote Originally Posted by maferv View Post
    How can I test how much ram it is actually able to cache?
    What software should I use to accomplish this task in MS-DOS or Win9x?
    (...)Could I select which part of the RAM I use for software and use the rest, the non-cacheable part as a ram disk, for instance?
    Attached Images Attached Images

  4. #4

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    I'm not sure how System Speed Test tests RAM, but it would look like it it's not touching RAM above 128MB. So provided you stay below 128MB usage there is no slow down.

    It says it wont run in a DOS window/multitasking environment. I don't know whether this means it wont run or it wont provide accurate results. If it will run, you could try opening enough programs then load it, to to force it to do the test above 128MB. I'm not sure if this will work though, you would need a control test where it accessed RAM below 128MB while it's in a multitasking environment. And you would need to ensure the program would get the same CPU time for both tests. You may at best get a qualitative test rather than a quantitative test. Alternatively disable the cache, and run the test to get an idea of speed.

    The datasheet states "Support SDRAM 6-1-1-1(-2-1-1-1) Burst Read Cycles". So:

    6+1+1+1+2+1+1+1 = 14 cycles for every 8 memory accesses or 1.75 cycles on average for each memory access.

    14.28Mhz (70ns) = 14,280,000 clocks per second 64 bits per line =

    913,920,000 (0.91 billion) bits per second (in bytes, ~109 MB/s)

    So for 70ns SDRAM ram at 6-1-1-1(-2-1-1-1) timing we get (109 MB/s)/1.75 = ~62 MB/S
    That is, the absolute maximum under ideal circumstances.

    I think that's right. Please someone correct me if I'm wrong, I have the suspicion I've missed something. Even at half that rate, it's going to be faster than paging to any Pentium era HDD.
    Looking for: OMTI SMS Scientific Micro Systems 8610 or 8627 ESDI ISA drive controller, May also be branded Core HC, Please PM me if you want to part with one.

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