# of Cores vs. amount of Ram

Discussion in 'Mac Pro' started by spaz8, Apr 4, 2007.

  1. spaz8 macrumors 6502

    Mar 3, 2007
    I've tried doing some research. Could someone explain to me the relationship between the amount of ram in your system and having 4, or 8 cores.

    Example, I have an old DP G4 1.25 with 2GB of ram.. so 1Gb per proc.. is there a minimum, or ideal amount of ram per proc?.. I was surprised to see u could configure the 8-core with only 1 gig of ram, are u starving the procs at that point?

    Is 4 gigs of ram (the min i want to have) different in a 2 core, 4 core, or 8 core system. thanks for your answers.
  2. rhoydotp macrumors 6502


    Sep 28, 2006
    although one can affect the other in some way, there is no hard rule as to how much RAM you need for how many CPU/cores you have. CPU's have their own cache that they use for faster transactions.

    more memory means that you have lots of programs that you can run so when the CPU needs to get the info it will be faster. the RAM will not be split by processors.

    more processors/cores means you can calculate more instructions. thus making it run programs faster.

    this is not comprehensive and i suggest you go read some more via wikipedia or "google". hope this helps a bit ;)
  3. Schroedinger macrumors regular


    Feb 12, 2004
    Baltimore, MD
    One way to think of this that helps is to think of extra physical processors as virtual processors. If you had a cpu that acted like 8 cores even though it physically only had one, how would that effect your views on minimum RAM necessary.

    If you're going to be running any kind of program that will actually make full use of the 8 cores you're going to be needing 4 or 8 gigs of ram anyway. If you run an 8 core system with 1 gig of ram using average software, the bulk of those cores are not going to be used.
  4. spaz8 thread starter macrumors 6502

    Mar 3, 2007
    Thanks for your help! though i welcome more info.. I will be running apps that will max out all 8 cores.. and potentially all 4 gigs of available ram to these 3d apps.. i just wasnt sure if with the 4 and 8 core systems Ram got diced up amoung the processors , or if it was still a big "pool". Thats where the 1 gig of ram per proc.. question stemmed from.. if id be castrating the system by not having enough ram per proc to keep them working and well fed with data to crunch.
  5. osx-linux macrumors member

    Apr 4, 2007
    RAM is a big "pool" to any multi-cores machine, 4,8,16...128 cores etc.

    For the mac pro if you are *really* crushing the data in and out, you may want to ensure you have 4 matched chips, eg: 4-1GB ram chips. or 4-2GB ram chips etc etc.

    In fact, if you only have 2 chips (as the default mac pro ships) you are cutting your peak theoretical memory bandwidth in half (only able to use 2 out of the 4 channels). So, you'll want four FB-DIMMs so that you can run in quad-channel mode. Again this is only if you are really moving data around.

    hope this helped.
  6. spaz8 thread starter macrumors 6502

    Mar 3, 2007
    thanks osx-linux.. and yes I was looking at getting 4x1gb matched sticks or 4x2gb sticks if there was a compelling arguement to.

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