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Memory slot placement

By flycpd ยท 4 replies
Nov 1, 2008
  1. I have been building computers for years and never found a reason for the placement of the memory slots on a motherboard. If you look at a board that uses an Intel CPU, the slots used are1-3 and/or 2-4. If you look at a board that uses an AMD CPU however, the slots used are 1-2 and/or 3-4. Does anybody know why this is? No, I'm not trying to make a better motherboard, I'm just curious enough to finally ask.

    Thanks for any info anyone can give.
  2. CCT

    CCT TS Evangelist Posts: 2,653   +6

    'If you look at a board that uses an AMD CPU however, the slots used are 1-2 and/or 3-4.'

    refer to the MSI K9N - which see;


    Dual channel with slots 1/3 or 2/4.

    Assuming that you installed 2 Gb in 4 modules of dual channel ram and it is used from byte 0 to 2047 linearly, then assuming that the average 2 Gb ram install running XP uses about 50% of the Ram running avg8 (as example), you would get heating in ram modules 1 and 3 and none to speak of in 2 and 4.

    Thus, heat separated components and better cooling.

    My opinion.
  3. futbol94

    futbol94 TS Rookie

    i also wondered this too.
  4. CCT

    CCT TS Evangelist Posts: 2,653   +6

    Yes - I would think so since it is what you asked!

  5. almcneil

    almcneil TS Guru Posts: 1,277

    It's the Microprocessor Architecure

    I know the anwer. I'm an engineer and it has to do with the microprocessor architecure. Not all micros access the memory the same way.

    In a nutshell, memory read/write operations (called "memory fetches") are time consuming. The microprocessor has to wait on the meory to respond as it's slower than the ultra fast microprocessor. To help speed up overall processing, the micro alternates its memory fetches between memory chip. Why sit around waiting for the first write to complete to access the next memory location on the same chip? So it memory maps the chips in an alternating fashion. This way you write the first memory location on one chip, the next on the other. While one the first is in progress, you can write the next value on the alternate chip because in the meory map, that the next location. Intel alternates the RAM chips 1-3 and 2-4 whereas AMD does it -12 and 3-4. That's all.

    -- Andy
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