Hi, here's one for all you tech experts: I have an older iMac, early 2008, that I'm trying to squeeze for its last drops of life. I'm planning on installing an SSD, but first, I'm maxing out the RAM. I already have 4GB, the official max, but all over the net there are reports of people having success with 6GB (4 + 2). The RAM already in the machine is two Crucial 2GB sticks: CT25664AC800: DDR2 PC2-6400 CL=6 Unbuffered NON-ECC DDR2-800 1.8V 256Meg x 64. My new stick is also Crucial, 4GB, bought it from a fellow who bought an 8GB kit but realized he could only use one of them in his identical machine. Apparently he had success. Specs: CT51264AC800: DDR2 PC2-6400 CL=6 Unbuffered NON-ECC DDR2-800 1.8V 512Meg x 64. So except from the 256Meg x 64 and 512Meg x 64, they seem identical. I've never had problems with Crucial hardware before, and the other matched stick in the pair works it this other guys iMac. I've tried the 4GB stick alone in both the left and right bank, and also in both positions with a 2GB stick in the other one. All I get is a black screen, and series of three beeps that repeat infinitely (- I assume, I can only bear the sound for a minute or two.) I can hear the CD drive spinning up, otherwise nothing is happening. Back to 2 + 2 GB sticks, all is fine. Does anyone have a clue? Bad stick, or something that can be worked out? Is it worth the hassle going from 4 to 6 GB? I'm running Yosemite on it, it's not exactly speeding along, but it works. Fire away, geniuses!