ioreg -p IODeviceTree -n memory -S | grep ram-
If the ram-layout-architecture value is 1, then you have a 128-bit bus; if it is 2, you have a 64-bit bus.
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I just got my iMac G5, and when I bought it I assumed I could just add any old compatible memory and it wouldn't affect performance. However, it appears that you need two DIMMs of the same composition to get a 128-bit memory bus instead of a 64-bit memory bus. According to macbidouille.com, this can yield up to a 38% increase in the performance of Xbench memory tests. Many people have bought RAM of the same size but different composition, and they are getting a 64-bit bus. To dispaly the RAM bus size, run the following command:
If the ram-layout-architecture value is 1, then you have a 128-bit bus; if it is 2, you have a 64-bit bus.
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Check the RAM bus size on G5 Macs
I have two questions:
Check the RAM bus size on G5 Macs
You must have both RAM slots filled in order to get a 128 bit bus. It is basically 64 bits per ram slot, and if the chips are close enough in spec the machine 'syncs' them so that it can use them as a single 128 bit wide channel rather then two 64 bit wide channels.
Check the RAM bus size on G5 Macs
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?
Check the RAM bus size on G5 Macs
Here's what Apple has to say about this:
Check the RAM bus size on G5 Macs
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... :-)
Check the RAM bus size on G5 Macs
Regarding the two posts above: As long as you have paired sticks of RAM (i.e. even numbers of the same sized sticks of RAM), the architecture will be able to use a 128-bit datapath on the bus.
Check the RAM bus size on G5 Macs
(I just love responding to my own post :-p)
Check the RAM bus size on G5 Macs
In my brand new dual 2.5GHz G5, the above mentioned command returns nothing. In other words, "ram-layout-architecture" does not exist in the IO registry. Also, any unpaired sticks that are installed are simply ignored. Apparently that machine can not deal with 64 bit memory widths.
macbidouille script link
macbidouille.com also offers a link to a script that will do the check (for those afraid of the terminal):
http://www.macbidouille.com/downloads/testbusG5us.sit
macbidouille script link
Hi, little late on this thread but... |
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