Hi, during the last two months I felt like living in Commodore heaven at the University, because the building where I work is being repaired and a lot of old stuff is turning up :-) I try to take the Commodore 8bit stuff with me of course, but some other equipment has to go. Today I tried to find out if these old Sirius or Victor MS-DOS computers are worth anything, and a Web search returned Cameron's Secret Weapons page as a result. It seems these machines were designed by Chuck Peddle after he has left Commodore and this makes them very interesting of course. I knew before that the disk drives of the machines use variable speed technology similar to the early Macs and that some sort of GCR coding was used. But I also found a dump of the Victor's GCR ROM on the net today, and compared it to the GCR ROM of 4040 and 8050 drives: they are extremely similar, the address map is a little different and in one part of the ROM one bit is permanently set, but otherwise the contents are just the same. It almost looks like this ROM was "borrowed" from CBM machines :-) I guess I will have to have a close look at the hardware of these computers, if there are any other similarities to CBM 8bit hardware. Did CBM have a patent for the GCR technology or maybe the speed zone implementation with the variable bit clock? Why did others always use variable spindle speeds instead? It's probably easier to design the data recovery circuit for a fixed clock, but a variable speed drive also isn't that trivial... Also, it's a while since I tried to understand what the GCR ROM actually does in a 8250: I think it looked like being able to convert a whole byte in one direction, but only half a byte into the other one. Can someone please confirm if this is correct or not? Nicolas - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
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