Upgrading the RAM on an iMac G5...

Posted:
in Current Mac Hardware edited January 2014
Alright- so I came across some more money and I want to upgrade my new iMac's RAM to 1gig.



I ordered it with a single 512 chip and what I'm wonder is what do I have to get to take advantage of the 128bit memory bus that is enableled if you have 2 "identical" chips.



How identical do they have to be? As long as they're both 512 DDR400 chips is this fine?



Thanks for the help!

-taco

Comments

  • Reply 1 of 5
    Ive just ordred a new imac and was wondering about the same thing. I found out that as long as the same amount and speed e.g 2x 256mb 400mhz its fine.
  • Reply 2 of 5
    Quote:

    Originally posted by tacojohn

    Alright- so I came across some more money and I want to upgrade my new iMac's RAM to 1gig.



    I ordered it with a single 512 chip and what I'm wonder is what do I have to get to take advantage of the 128bit memory bus that is enableled if you have 2 "identical" chips.



    How identical do they have to be? As long as they're both 512 DDR400 chips is this fine?



    Thanks for the help!

    -taco




    nope that is not enough. you need to match the timing and cas latency as well. they are usually rated with a series of 3-4 numbers such as 3/2/2/4 or 2.5/2/2/4. these specifications must match exactly for the imac to take advantage of the 128-bit interface. if the timings dont match they simply wont run in parallel. you will still have your 1 GB of ram it just will be running on two 64-bit interfaces instead of a unified 128 bit interface.

    or something like that
  • Reply 3 of 5
    Someone know the latency and the chips of RAM which is shipped with the stock iMac ? I have bought a pair of Samsung 512MB DDR400 CL3 which is technically with the same specification, speed and latency. But the iMac won't be arrive to the shop I will buy from until next week, anyway I bought the RAM and have them running for a few days on my brother's PC see if it have any problem before put it on my new iMac. The pair cost me around US$175.(I'm in Hong Kong, not US)



    The waiting these weeks is tooooooo long....can't wait anymore.
  • Reply 4 of 5
    Quote:

    Originally posted by CheapFrag

    you will still have your 1 GB of ram it just will be running on two 64-bit interfaces instead of a unified 128 bit interface.



    There are no benchmarks on what sort of speed loss is involved in running as two 64bit busses ( rather than a 128 bit bus ). But I think it really boils down to having a little less efficiency. I dont think it will be noticable in daily usage, a couple of % at most.
  • Reply 5 of 5
    Quote:

    Originally posted by mmmpie

    There are no benchmarks on what sort of speed loss is involved in running as two 64bit busses ( rather than a 128 bit bus ). But I think it really boils down to having a little less efficiency. I dont think it will be noticable in daily usage, a couple of % at most.



    I have seen xbench memory benchmark improvements of 30% or so. but unless you are doing hardcore stuff that can utilize this throughput you will not notice it. also, i read an interesting article (sorry no link) that stated you can in some cases get the 128bit memory bus with identically timed RAM but of DIFFERENT sizes. I'll see if i can find a link for that. The latency and timing does have to be exactly the same though.



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