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Check the RAM bus size on G5 Macs
Authored by: stilesja on Oct 11, '04 01:30:54PM

So, I am curious. I ordered the single 512MB stick from Apple planning on adding another 512MB sick on my own. How do I know what configuration to order so that I can have a 128MB memory bus?



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Check the RAM bus size on G5 Macs
Authored by: floh on Oct 11, '04 02:39:56PM

Here's what Apple has to say about this:
[http://developer.apple.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G5/iMacG5/04_Expansion/chapter_5_section_1.html#//apple_ref/doc/uid/TP40001433-CH208-BBCJADAF]

Basically, you need two technically identical DIMMs to get a 128 bit memory bus. this means, that the two dimms need not only have to have the same physical size (i think also number of chips since there's different possibilities of composing, say 256 megs from different chips) but latency values must be the same, too. safest is to get two identical DIMMs from the same manufacturer.

But ... I have seen different oppinions about this ... german computer magazine c't says, that increase of performance in real world environment is about 0-4%, so far from being noticeable. Now c't is the only computer magazine I would trust at least as far as I can throw the magazine around here, but they fail to mention what they think "real world" means and the article lacks details about test environment, etc. Still I'd be careful to overestimate the effect of identical DIMMs in single cpu systems.



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Check the RAM bus size on G5 Macs
Authored by: stilesja on Oct 14, '04 01:12:33PM

Well, I ended up ordering my memory from crucial.com as they had a specific catagory for iMac G5 20inch memory, and I thought if there was a chance of getting the right memory to make it 128bit that would be it. I had talked to several discount sellers and none could guarantee what memory I would get so I went ahead and paid about $30 extra and got it from crucial. Turns out that after installing it my bus is 128 bit so I am happy! Not that I really would have noticed a difference... :-)



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