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I've recently acquired an aging iMac (G3/500 DV SE, Summer 2000) with its original 128Mb RAM out of a possible 1Gb. I'd like to replace the single 128Mb DIMM with 2 x 512Mb DIMMs. I know these need to be 168-pin PC100 SDRAM, 10ns or faster, and I know that PC133 is meant to be backwards compatible with PC100.

However I tried 2 x 512Mb DIMMs the other day and the iMac wouldn't boot up (just stayed on a grey screen). Replacing the original 128Mb DIMM brought it back to life.

I read on this page that "just because RAM meets the minimum listed criteria does not mean that it will necessarily function as intended in a particular Mac". This is a bit of a worry. How can I buy RAM off eBay or even in a shop with any confidence? Nobody selling RAM in 2009 is going to have tested it on a 2000 vintage iMac. Is there any way to tell in advance if a given stick of RAM is going to work, e.g. by its maunfacturer, specs, part number, etc.? Or do I simply have to resort to the much more expensive and time-consuming approach of trial and error?

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up vote 1 down vote accepted

You could try the Mac memory scanner from Crucial. It may be able to tell you exactly what memory you can get. The website mentions a money-back guarantee if you purchase the memory through their website and it does not work.

If you don't want to buy it from the website at least it will give you a clearer picture of exactly what you need.

iMac G3/500 is listed on the site, so it should work.

This is what will probably come up:

512MB Part #: CT223786 • SDRAM, PC133 • CL=3 • Unbuffered • Non-parity • 133MHz • 3.3V • 64Meg x 64 • • more details

512MB Part #: CT260476 • SDRAM, PC133 • CL=2 • Unbuffered • Non-parity • 133MHz • 3.3V • 64Meg x 64 • • more details

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This year (2015) I bought two 512 MB memory modules from Other World Computing for an iMac G3 500 and they work flawlessly (as advertised). I have installed Debian GNU/Linux on it and now I can run Firefox without frustration. It cost me $31.58 plus $2.99 shipping to Sweden. Highly recommended.

Item number: OWC100SD512328

Here are the installation instructions:

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The original RAM I tried was ECC. I tried some non-ECC RAM (as the one that came with the iMac was), and it worked fine. Maybe I just got lucky, or maybe that's the whole answer. Either way, I hope this finding helps someone else.

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