Q I have upgraded my iMac with two 4 GB memory modules from a reputable supplier. However when those are installed, singly or as a pair, my Mac keeps falling over. Sometimes it simply throws a kernel panic, and when I try to waken it from sleep it may freeze, or throw a panic. Is this a known problem with Yosemite?

A Yosemite does not appear to have a propensity for throwing panics in this way, nor is it known to make Macs any more pernickety of their memory.

Kernel panics like this are almost invariably the result of hardware problems, and you have demonstrated clearly that the hardware responsible is your two new memory modules. There is an outside chance that problems might resolve after a firmware update, if one is offered in the App Store’s Updates.

If you still suffer the same panics and freezes, then you have no option but to return the memory to its supplier. Check with them the exact model number of your iMac, such as that given in System Information, to ensure that the specification is correct.

Updated from the original, which was first published in MacUser volume 27 issue 24, 2011.