Harder than it was alleged.

My Problem

I wanted to expand my memory, so I purchased the appropriate units from Other World Computing and followed the instructions on this web site.

My Fix

When I installed the memory--checking that the frequency matched the original memory, as suggested on this site--the computer did not reboot, but gave beeping tones in groups of 3. I called Apple, who had a few suggestions, then concluded that I should bring the iMac to the store. I called Other World Computing, who got it right. First, I had to reconfigure the existing memory, moving each chip up one slot and install the new memory chips, then I had to depress the option, command, p and r keys and push the power on button to reboot. This requires long fingers and some skill at twister. After this, everything worked.

My Advice

Other World Computing not only has good hardware at good prices, but they stand behind their products with excellent tech support.