I've got a nice 6" wafer, though it isn't completely round... one... end? (what the hell do you call it on a circle) is flat. It's also already been etched, and each of the dies look to be 50mm. Can't say I know what the hell it is. I got it in my Sr. year of HS... so 2000, from VTC, Inc. It's some MN company that a classmate's dad worked at, and we got to go on a field trip, though I was elsewhere at the time, and unable to go. As to why it's round? Look at the link someone provided. I just wanted to brag about my 6 incher.... I hope that doesn't sound wrong.
-SammyBoy