eesrajm@cc.brunel.ac.uk (Andrew J Michael) (02/13/91)
I have just answered my own question about coping with hard disks which do not have a constant number of sectors per track, and in doing so have discovered something which might be of interest to others, so I'm posting this. A resume - I recently bought a Rodime 3259A 3.5" IDE winchester, which is 259Mb unformatted, and should format to 213Mb. The specs for this drive are as follows: No of tracks: 1235 No of heads: 9 Sectors per track: 41 (outer zone), 34 (inner zone). As you can see, this drive does not have a constant number of sectors per track, which makes a nonsense of the normal DOS/Xenix disk parameters. I didn't know what parameters to give Xenix when formatting it. However, a telephone call to Rodime got me a rather interesting book called the RO3000A Guide to Installation (Part No. USM 00226-8). It seems that to get the drive to format correctly, the parameters given to DOS or Xenix should be: No of tracks: 990 No of heads: 15 Sectors per track: 28 These don't bear much resemblance to the real parameters; apparently the drive "translates" requests to keep DOS and Xenix happy. It is rather interesting to note that the fake parameters may be any combination of numbers which multiply to give the correct total capacity ! This means that the DOS/Xenix cylinder number limit is irrelevant, and I understand that Rodime aren't the only manufacturers of drives which behave in this way, so even bigger drives could work OK under Xenix. On a second point, Rodime claim a transfer rate of up to 4Mb per second concurrent (reading from the disk) and 6Mb per second non-concurrent (i.e. reading from the onboard 64k cache). It certainly seems a very fast drive; much faster than the 100Mb Conner which I used briefly. And since it does its own bad sector management, you don't need to allocate any bad tracks. Pretty neat. Andy Michael -- Andy Michael (eesrajm@cc.brunel.ac.uk) "You might think that. I 85 Hawthorne Crescent couldn't possibly comment." West Drayton Middlesex UB7 9PA