Well I figured this is probably the best place to ask. I got an atari 600xl a year and a bit ago, didn't come with a power supply and didn't get one till about 6 months ago. I got some cart games and software to play around with and when I was messing with the self-test, the RAM test kept going for a long time, up to 48 blocks of RAM were tested. Concerned that there was a bad RAM chip, I opened up the machine and discovered a massive Applied Engineering RAM daughter card installed over where the stock RAM would've been. I thought Applied Engineering only produced upgrades for the Apple II, Mac and Amiga machines? I looked up the data sheet for the RAM chip type on the board, and it turns out there's a bunch of 4K chips that add up to 64K total. Can someone shed some light and tell me what the hell have I got? An apple II upgrade that was modified for a 600XL, or an actual AE stock product sold for the 600XL? Will post pics later when I crack the machine open again.