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Thread: 386 BIOS - High and Low vs Odd and Even

  1. #1
    Join Date
    Dec 2012
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    Default 386 BIOS - High and Low vs Odd and Even

    I have a 386 system with an Award 3.03 Modular BIOS (32K each). It is split into High and Low. It is possible to substitute it with a BIOS marked Odd and Even? If so, which Bits correspond with which (I assume High = Odd, Low = even).

    Thanks!
    Geoff

  2. #2

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    if its from a motherboard with an identical chipset, its probably fine.

  3. #3

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    Quote Originally Posted by gepooljr View Post
    If so, which Bits correspond with which (I assume High = Odd, Low = even).
    You know what's likely to happen when you assume.
    PM me if you're looking for 3½" or 5¼" floppy disks. EMail “ ” For everything else, Take Another Step

  4. #4

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    Quote Originally Posted by Stone View Post
    You know what's likely to happen when you assume.
    well seeing as how he's correct, I don't think this is a valid application for your cliche

  5. #5

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    Disconnect your hard drive and try it. I'm assuming you are swapping in chips and not doing a flash on board. You don't want to brick your machine.
    If it doesn't boot to a disk error, you know it is wrong.
    Dwight

  6. #6
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    x86 boxes are little-endian, so it follows that, in a word-aligned memory scheme, the lowest-address bytes are the least-significant, hence, "even", the next higher address bytes are most significant, or "odd".

    Visualize the way the words (hex) 1234 and 5678 are stored in memory

    Code:
    0000 | 0001 | 0002 | 0003 | 0004 | 0005  <-byte address
      34     12     78     56     ..     ..
    This is in opposition to "big endian" schemes, such as used on the 68K CPUs, where the above data would be stored as 12 34 56 78 in increasing addresses.

    Both have their advantages and disadvantages. Little-endian schemes generally appear where words (or doublewords) need not be aligned to a specific address boundary.

    Early Unix ports across big- to little- endian architectures often ran afoul of this, leading to the so-called "nUxi" problem...

  7. #7
    Join Date
    Dec 2012
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    Portland Oregon
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    Thanks everyone for the help. I was able to get the different BIOS working, but it didn't really offer any new features.

    Geoff

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