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I have an original Mac Pro with 2 GB of RAM in it. Running Mountain Lion on it is a bit painful - lots of paging. I happen to have 4 GB of PC2-4200 ECC FB-DIMMs kicking about. What I wanted to know is will the Mac run with the slower memory, or will it throw a hissy fit?

The Apple tech specs at say 667 MHz, but nothing about slower.

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You can't use slower RAM. In fact I've had trouble with some manufacture's RAM even though it met the spec. You need to go to a site that guarantees any new RAM will work in a Macintosh.

I didn't think that the original Mac Pro could run Mountain Lion. I've got a Mac Pro 2.1, from 2007, that refuses to allow Mountain Lion to be installed. Did you hack this?

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When I said I had the Mac, really I meant one of the autonomous groups did and they came begging for RAM, so I'm not 100% sure of what they did. I believe it involved EFI firmware emulation. – Biggles Feb 20 '13 at 16:22

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