To help move them along, the Tandy 1000 is an interesting machine. I'm not sure about the straight 1000 model, but variants of the 1000 have DOS and even DeskMate (Tandy's windowing environment, which I believe was a tailored version of early MS windows) in ROM. Original IBM PC XT and AT machines are getting difficult to find (especially ATs, which it seems weren't produced in the same numbers as earlier models) and the Corona's are significant because IBM successfully sued them for copyright infringement for basically copying the ROM code verbatim and using it in their clones.