When you fill your office with vintage Macs, your co-workers might get the impression you collect them. Last week, a co-worker of mine brought me a Performa 640CD (DOS). Because this is one of the few DOS-compatible Macs made, I was glad to add it to my collection. After my initial inspection, I decided almost immediately to clock-chip it. It had a 68LC040 CPU running at 33Mhz. After consulting Marc Schrier’s excellent clock-chipping resource page, I found that I only needed to move two surface mount resistors on the logic board. I did this quite easily with a nice soldering iron. When I reassembled the machine, it almost completely booted the first time. I had to go back and add a heat sink I pried off of a Pentium 200 chip. Now, I have no instability. I installed DOS 7.1 on it and it’s running well. I want to replace the DX2-66 486 chip with a 100Mhz 486, but that may add to the heat too much. Add one more overclocked Mac to my collection!