sung@mcnc.org (Wayne Sung) (10/10/90)
There have been some discussions in this group recently about using HD floppies to replace 8 inch drives. I tried this using a 3.5 inch HD drive and here are some early results. Hardware: In general there are no hardware difficulties. If you looked at the pinouts of an 8 inch drive and a 5.25 inch drive you will find that many of the pins line up one for one. I happened to have an adapter board that converted between the two size ports so I did not have to make a cable. The drive that I got has an adapter to go from the 34 pins to a 34 card edge but either would have been ok. Two signal lines had to be accounted for. The 8 inch drive has a drive ready line which the smaller drives do not. In my case this line is sensed by the bios but the easiest way out is simply to keep it grounded. There is also a signal out of the 8 inch drive indicating that a two-sided disk is inside. Since there are no single sided HD disks, this line could also be grounded if I was to replace all my 8 inch drives. In mixing single side 8 inch and double side HD, it's trickier because the line is used during format sense. I presently have a jumper which has to be removed for single side disks. One interesting sidelight: the last set of 8 inch drives I had been using cannot step at 3 ms rates. These 3.5 units can, and are actually much quieter stepping at 3 ms than at 6 msec. Software: The formatters that I have don't exactly behave right. For one thing, they are set up for 77 tracks which wastes some 50-60k of space. They also don't seem to be able to format up to the highest sizes (presently 1.2M on the 8 inch system). I suspect the track layout has to be redone, since with the much smaller circumference there is less room for pad bytes and the 8 inch format has a lot of pad bytes. I did not have any difficulty reading the 1.44M size that had been formatted on another machine. Of course the DPB will also have to be adjusted to account for the extra tracks when I get to use them. If anyone would like more info let me know.