pritch@osu-eddie.UUCP (Norman Pritchett) (06/30/86)
Many thanks to the people who responded to my question about why three double-sided drives worked on my CoCo but four didn't. Also, tnx to all who suggested this disk driver and that to use double-sided drives with OS-9 but you missed where I said I use Dave Lewis' NEWDISK for that. I'm already doing it -- I was just a little confused why it worked. The eve before the responses started flooding in I checked through my technical reference manuals for the TRS-80 Models I and III and noticed the schematics for the Tandy drives differed from the ones I have on my CoCo (ok, that's obvious but you know what I mean). This is how I discovered that the coco controller was using drive select 4 on what the rest of the industry used for head select. That answered the question about whether not my not being able to get my 4th drive to work was a fluke or not -- all the responses to my posting confirmed it. My next question is why Tandy did things this way. I have a theory and I would appreciate it if someone could tell me if it is at all accurate. Looking at the signal assignments for the drive/controller connection I get the impression that only 3 floppy drives were allowed for initially -- drive selects 1 through 3 are grouped together but drive select 4 is way off by in another corner. When Radio Shack came out with disk systems for the TRS-80 Model I they wanted to support 4 drives but since drive select 4 didn't exist they picked one from the unused pins. The industry later assigned the head select signal (to Radio Shack's drive select 4) and drive select 4 (to an unused pin) but Radio Shack kept their interface the way it was for the Model III and for the CoCo (I assume R.S. initially sold the old Model I/III drives with CoCo disk systems). So if you use the original R.S. Model I drives you can support 4 of them; if you use anybody else's you can only support 3 but you have the option of double-sided operation with the proper drives and software. Is this close? -- Norm Pritchett, The Ohio State University BITNET: TS1703 at OHSTVMA Bellnet: (614) 422-0885 UUCP: cbosgd!osu-eddie!pritch CSNET: pritch@ohio-state ARPANET: NPRITCHETT%osu-20@ohio-state (or) pritch@ohio-state