Mixing PC133 and PC100 memory

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Level 1

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Mixing PC133 and PC100 memory

I just bought a G4 (Digital Audio) 466. I wanted to add more ram, so I bought a PC 133 512 card. When I checked the system profiler, it shows two cards already installed, one a 128 PC 133, and the other a 128 PC 100. It's working fine, and with the new 512 in it, it's working fine. I believe I read somwhere that with a PC 100 card in it, it will only allow the other PC 133 cards to run at 100 mHz; only as fast as the slowest component. So my question is, is this true? And, is it a noticable difference? If I remove the PC 100 card and just go with the two PC 133 cards, for a total ram of 640 @ 133 mHz, instead of 768 ram @ 100 mHz, will it be faster? Or should I stick with the higher ram count until I can replace it with another PC 133?

G4 Digital Audio 466 mHz, Mac OS X (10.3.9), 768 MB ram

Posted on Feb 21, 2007 5:04 PM

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Answer 1

Best reply

fragmore

Level 3

661 points

Feb 21, 2007 5:15 PM in response to Zimlick

Your computer calls for 133 per Mactracker [free download].
My computer calls for 100 but I use 133 because it was easier to find, Thc computer will only run the ram at 100.

If your computer is running fine with what you have, don't worry.

My understanding is that the computer board calls for the RAM speed, thus if it calls for 100 then the 133 will run at 100. The ram only responds to the computer not the other ram. However, at the low cost of ram you could easily replace one slower stick with a new 133 one. Go for a 512mb module then you will see a real difference.

Confusing, go to www.crucia.com and ask their tech support.

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Answer 2

Feb 21, 2007 5:23 PM in response to Zimlick

My understanding is that the Mac is designed for RAM with a speed of 100MHz. If you replaced all your RAM with PC133 modules, it would still run at 100MHz. RAM is backward compatible, that is, PC133 RAM can operate at 100MHz. However, PC100 cannot operate at 133MHz speeds.

PC100 RAM is in short supply & mostly used RAM. Most likely purchasers buying new RAM for a PC100 application, will get PC133 RAM from the supplier.

Thus, stick with your current total of 768MB.

 Cheers, Tom

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Answer 3

Zimlick Author

Level 1

0 points

Feb 21, 2007 5:38 PM in response to Texas Mac Man

The G4 Digital Audio was the first in the G4 series to upgrade to a 133 mHz buss, so I know using PC 133 is optimizing it's potential. I'm wondering if that PC 100 card in my machine is slowing down all three cards.

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Answer 4

Jeff

Level 6

12,058 points

Feb 21, 2007 7:45 PM in response to Zimlick

If your computer has a 133 MHz FSB speed, you should use PC-133 SDRAM, which has 7.5ns or 7ns chips on the DIMM. Some PC-100 DIMMs have chips with a 10ns speed, which you definitely wouldn't want to use on a 133 MHz bus. Higher quality PC-100 SDRAM having 8ns chips is usually good to 125 MHz, so you could probably use it without problems - but I wouldn't recommend doing so.

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