On Sat, 15 Aug 1998 11:38:47 +0000, you or Dan Doore <[EMAIL PROTECTED]> wrote:
>> So. Why did they have two controllers then? There must have >> been a reason. > >I was reading an old issue of Format, where on Nev's Help Page there was >a question about getting the error 'FORMAT DATA LOST' when copying >between two drives on the Disciple/PlusD, and this was due to the >(single) disc controller getting out of sync. It was mentioned that Sam >does not suffer from this because it uses two. > >Nev might be able to shed more light on the matter, since he wrote the >article :-) > Yup, the problem is/was that with only one controler the 1772 internal registers for track/sector etc get updated from data held on the disk. As you switch from drive to drive the registers get out of sync and the 1772 thinks you should be on one track when you are in fact on another. This problem was fixed in unidos (remember that ?) by always restoring the registers from memory when ever the drive was switched. Sam could do exactly the same but it never was as the dos for sam was derrived from gdos rather than unidos and so did not save/restore the internal registerd. hth Nev's help pages eh ? that was a long time ago in another life.
