I saw a few different threads on this, none very recent, so here is my own take, hopefully comprehensive. This is for a 24" alum iMac (mid-2007).
1. After looking at the instructions, I thought that I would save myself some trouble by simply bringing the iMac to the edge of the desk, titling the monitor all the way back, and sitting on the floor underneath to access the memory compartment. I ended up laying it down on the desk, per instructions, since dealing with the issues described below was much easier that way (better stability and visibility).
2. Removing the memory bay cover is an ordeal. The screw is "captive," which means it does not come all the way out, it only loosens. Unfortunately the cover itself is fitted unevenly and overly tightly. I found that running a flathead jewler's screwwdriver under the lip of the cover to pry it loose worked. I was never sure whether I was going to pry it loose or break it, it is very sticky. Poor engineering here on Apple's part.
3. There will be dust inside the compartment. I don;t know enough to say if compressed air would be a good idea here or not.
4. Placing the new memory is difficult. You have to push it very, very firmly into place, sliding along a channel on either side. The manual mentions a "click" when the memory is placed but I didn't hear that. Once the memory is in as far as it will go with reasonable force, you push a bit harder until the back edge of the memory board is slightly deeper than the screw receptacle in the middle.
5. Beacause of this, memory with slight irregularities may not fit when it would in a PC. One of my memory boards (Crucial) had a protruding thickness on one side that made it impossible to seat.
6. If you hear a series of tones when the iMac is turned back on, the memory is improperly inserted or incompatible.
1. After looking at the instructions, I thought that I would save myself some trouble by simply bringing the iMac to the edge of the desk, titling the monitor all the way back, and sitting on the floor underneath to access the memory compartment. I ended up laying it down on the desk, per instructions, since dealing with the issues described below was much easier that way (better stability and visibility).
2. Removing the memory bay cover is an ordeal. The screw is "captive," which means it does not come all the way out, it only loosens. Unfortunately the cover itself is fitted unevenly and overly tightly. I found that running a flathead jewler's screwwdriver under the lip of the cover to pry it loose worked. I was never sure whether I was going to pry it loose or break it, it is very sticky. Poor engineering here on Apple's part.
3. There will be dust inside the compartment. I don;t know enough to say if compressed air would be a good idea here or not.
4. Placing the new memory is difficult. You have to push it very, very firmly into place, sliding along a channel on either side. The manual mentions a "click" when the memory is placed but I didn't hear that. Once the memory is in as far as it will go with reasonable force, you push a bit harder until the back edge of the memory board is slightly deeper than the screw receptacle in the middle.
5. Beacause of this, memory with slight irregularities may not fit when it would in a PC. One of my memory boards (Crucial) had a protruding thickness on one side that made it impossible to seat.
6. If you hear a series of tones when the iMac is turned back on, the memory is improperly inserted or incompatible.