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Forgive my ignorance...

post #1 of 7
1/4/02 at 8:59pm
Thread Starter 
What's the difference between SDRAM and DDR RAM? And this is the stupider question: can I use the 1Gig of SDRAM I have in my current G4 in the new PowerMacs with DDR RAM? Of course I would be expecting RAM performance decreases, but would I have to just kiss the current 512MB chips I have in my current machine goodbye?
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post #2 of 7
1/4/02 at 9:12pm
"Forgive my ignorance... "
Okay, your forgiven

Although I'm no ram expert, I'd say definatley, no. The difference between them? Don't know on a technical level, but DDR is apparently significantly faster.
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post #3 of 7
1/4/02 at 9:17pm
[quote]Originally posted by X704:
<strong>"Forgive my ignorance... "
Okay, your forgiven

Although I'm no ram expert, I'd say definatley, no. The difference between them? Don't know on a technical level, but DDR is apparently significantly faster.</strong><hr></blockquote>

Double the speed actually: Double Data Rate RAM

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post #4 of 7
1/4/02 at 9:18pm
When information is stored in memory and then accessed it does that in a 'cycle'. Regular RAM runs in one cycle. The processor loads information into memory, memory stores it, and then the processor fetches the information from memory. All of this happens at the system BUS speed, that is why when you have a 133MHz system bus you also have 133MHz ram. If you had DDR ram (Double Data Rate) the RAM 'double pumps' the information, in other words instead of just receiving and releasing information once a cycle, it does it twice. Therefor if you have a 133MHz system, and DDR ram, the path between the ram and processor is actually running at 266MHz due to the memory double pumping the information.

Hope I explained this correctly...does this make sense to you?

I know what it means just not sure how to explain it.
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post #5 of 7
1/4/02 at 9:20pm
DDR RAM and SDRAM are not interchangeable. As with all previous generational changes in RAM technology, all your old stuff is useless.

On the upside, DDR RAM transfers two bits on every clock cycle rather than one as in SDRAM. This means the bandwidth to/from memory is doubled, which will make a huge difference in processor intensive applications -- especially in all AltiVec code since the AltiVec usually spends its time waiting for memory.
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post #6 of 7
1/4/02 at 11:21pm
Some chipsets will accept either, not both at the same time. You could use your SDRAM and save your dough (you'll need too after buying a new powermac) for loads of DDR after all these RAM-manufacturer mergers stop fscking with RAM prices.
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post #7 of 7
1/4/02 at 11:28pm
I've been wondering this too...thanks for taking the time to explain it. Definitly sounds like something they should implement ASAP.
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