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RAM Upgrade: concerned about PC100/PC133 compatibility

post #1 of 4
11/7/09 at 10:48pm
Thread Starter 
Okay. Here's the story. My girlfriend has an old 2003 iMac (800MHz, pre-USB 2.0, 15"), but it's slow. She can't afford to buy RAM at the moment. It uses PC133 RAM.

I have an old 2002 iBook kicking around that uses PC100 RAM, with an extra 512MB chip in the user-accessible slot. I thought of trying the slower memory in her machine.

Would this pan out? I have heard all over the place that faster memory works in slower machines by underclocking itself, but what is the opposite like?

In the event that sticking PC100 memory in a PC133 system is not advised, are there any software hacks that might slow the PC133 system down to PC100 speeds (because I imagine upgrading from 256MB to 768MB of ram is more significant than underclocking the speed of the memory) so that it works?

Thanks in advance.
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post #2 of 4
11/8/09 at 6:46am
No, you can't put PC100 RAM into a PC133 machine. It's the bus that controls the speed, and in a system using PC133 RAM, the bus is too fast for PC100.

You are correct that a RAM upgrade will do wonders for overall system speed. What's the problem though? Surely PC133 RAM is crazy cheap on eBay these days?
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post #3 of 4
11/8/09 at 11:42am
Thread Starter 
It's cheap on eBay, yes. But before I go out and spend 20$ on another chip, is there any reasonably safe way to downclock the system bus so that it would accomodate the pc100 chip I already have? Perhaps in Open Firmware?
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post #4 of 4
11/8/09 at 11:48am
Quote:
Originally Posted by speed_the_collapse View Post

It's cheap on eBay, yes. But before I go out and spend 20$ on another chip, is there any reasonably safe way to downclock the system bus so that it would accomodate the pc100 chip I already have? Perhaps in Open Firmware?

Not that I'm aware of, sorry.

Maybe someone will pop in here saying they know you can do it; in the mean time I suggest a Google session. Also look for information on how to overclock, as said information should enable you to underclock as well, it's just that you're more likely to find discussion of how to over- rather than under- clock.

Good luck! Let us know how you get on.
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