G5 iMac RAM. Needs two identical sticks?

Posted:
in Current Mac Hardware edited January 2014
hi everyone,

at the moment this iMac hass 256mb of RAM, but clearly i want to increase that. What i had planned to do was buy a stick of either 512mb or 1GB (depending on how far i can stretch the budget).

But ive read somewhere that the G5 iMacs need to have the same sized stick of RAM in both their two slots. This would mean buying 2x512mb sticks. Which would give me the hassle of selling the current 256mb chip in it!



Is this true? It seems pretty unlikely to me, but i figured someone here would know.



that's it

Comments

  • Reply 1 of 7
    brunobruinbrunobruin Posts: 552member
    Quote:

    Originally posted by spiers69

    Is this true? It seems pretty unlikely to me, but i figured someone here would know.



    It's true only in the sense that matched pairs operate with a 128-bit data path, while a single stick or unmatched pair run on a 64-bit path. The pairs have to be matched not only in size, but in latency and devices and so on - any two same-sized sticks won't necessarily give you 128-bit goodness.



    I've read conflicting reports on the actual benefits of 128-bit, however. The first news seemed to be that it provided a speed boost, but I've also seen benchmarks that show the benefit to be negligible. So I have the stock 512 in one slot and added a 1GB stick in the other.



    RAM in the G5 towers must be installed in pairs.
  • Reply 2 of 7
    spiers69spiers69 Posts: 418member
    can you (or anyone else) explain in simple terms what this 64-bit and 128-bit data path stufff means?

    Will i be able to notice if my computer is running on a 64-bit data path instead of 128?



    OK. If i were to add a single GB chip (so id have 1256mb of RAM on a 64-bit data path), would that still operate better than if i were to buy a set of 512mb chips?



    Thank you
  • Reply 3 of 7
    bergzbergz Posts: 1,045member
    I'm not sure if this imac developer page applies to all current imacs (it's old), but is says:



    Quote:

    Note: The iMac does not use memory interleaving, so installing two DIMMs of the same size does not result in any performance gain.



    Here's the current one. Look through it:



    http://developer.apple.com/documenta.../eMac/eMac.pdf



    --B
  • Reply 4 of 7
    emig647emig647 Posts: 2,426member
    Quote:

    Originally posted by spiers69

    can you (or anyone else) explain in simple terms what this 64-bit and 128-bit data path stufff means?

    Will i be able to notice if my computer is running on a 64-bit data path instead of 128?



    OK. If i were to add a single GB chip (so id have 1256mb of RAM on a 64-bit data path), would that still operate better than if i were to buy a set of 512mb chips?



    Thank you




    128bit vs. 64bit data paths. On most sticks of ram (yes these) there are thousands of "mailboxes". Each of these mailboxes hold data and instructions. These hold the information for your programs and files etc. Each of these mailboxes are 8bits (or 1 byte). So 64bits can access 8 bytes while 128bits is equiv. to 16 bytes per clock cycle. So basically you are transmitting double the "information" from your ram to your cpu. This usually only works in the best case scenerio... hardly the medium case.
  • Reply 5 of 7
    spiers69spiers69 Posts: 418member
    ok. But id still be better with 256mb+1GB, rather than 512bb+512mb, right?
  • Reply 6 of 7
    brunobruinbrunobruin Posts: 552member
    Here's what Apple has to say about 128-bit:



    Quote:

    A 128-bit data path allows greater throughput than a 64-bit data path, in the same way that a 4-lane highway allows more traffic than a 2-lane highway. This allows the computer to manipulate large files faster. With a 128-bit bus, you would see better performance from the iMac when you have multiple applications open at the same time. On the fun side, you would also see some enhanced gaming performance.



    spiers69, my guess is that in your case it's probably a wash. The performance gain from using matched pairs is probably about as negligible as the difference between 1GB and 1.2GB of RAM. Once you get around the 1GB level, there's a law of diminishing returns. There's a huge difference between 256 and 512, less of a difference between 512 and 1GB, and even less between 1GB and 1.5, for example. It's not a linear progression. Although OS X WILL use as much RAM as you throw at it, especially if you have lots of apps or widgets open.



    I don't know that there's a strong argument either way. Of course two 512s are usually a bit cheaper than a single 1GB...



    Here you go, benchmarks.
  • Reply 7 of 7
    lundylundy Posts: 4,466member
    Quote:

    Originally posted by spiers69

    ok. But id still be better with 256mb+1GB, rather than 512bb+512mb, right?



    Yes, but only because it is more memory.
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