G5 and Mac Pro towers actually require the installation of pairs of modules, though most other Macs will allow the use of an odd number, with the proviso that you won't get the fastest possible performance from them. Crucial's website will tell you the specifics for your Mac. You will be surprised by how cheap RAM is, and also that you can still get it for old machines, giving them a new lease of life.
Before you buy, check the maximum RAM capacity of your Mac. You can download a free program called MacTracker (on this issue's disc) that will tell you the precise technical specifications of every Mac ever produced.
A blue and white G3, for example, can hold a maximum of 1GB of RAM in its four slots, so there's no point in buying more than that. A late G4 PowerBook can hold 2GB in two slots, and a first-generation Mac mini takes 1GB but only has one slot. You may end up replacing, say, a 512MB stick with a 1GB stick in certain models, making the original stick redundant due to lack of extra slots, but that's the way it goes in the fast-moving world of computing.
You can try sticking the old chips on eBay, but they might not be worth a great deal. Remember also that some iMacs and portables have one chip hard-wired so it's not user-replaceable, leaving only a single slot.
RAM capacities are improving, with new Mac Pros able to hold a whopping 32GB of physical RAM in eight slots, if you really need it. New MacBook Pros can hold 8GB but at this moment in time can only address 4GB, which is presumably an issue that will be fixed in an upcoming revision of OS X.
Common sense
Before upgrading your RAM or indeed any other part of a Mac, take the following precautions.
Shut down the Mac and wait five or ten minutes for any heat to dissipate. Then disconnect all its cables including the power cable. Take the battery out if it's a laptop. Touch a metal surface to discharge any static electricity you may have built up, to prevent it damaging the Mac's components.
Be firm but careful with the RAM sticks as they will need to be pushed into place, and avoid touching anything other than their edges.
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First published in MacFormat, Issue 203
Now read Which is the best word processor for your Mac?
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