On Thu, Apr 27, 2017 at 4:43 PM, Fred Cisin via cctalk <cctalk@classiccmp.org> wrote: > On Thu, 27 Apr 2017, Ethan Dicks via cctalk wrote: >> >> It's not impossible to find another TM-100-1 or replace it with a >> TM-100-2 > > Actually, the IBM 5150 PC originally (August 1981) mostly came with TM100-1. > It wasn't until about nine months later, when IBM released PC-DOS 1.10 (May, > 1982, which supported double sided drives) that they added TM100-2 > availability.
Ah. I had forgotten that detail. I only ever worked machines with double-sided drives. > Why not use the TM100-2? It will work for any of the single sided use, and > some versions of the operating systems supported double sided drives. > (On the Tandy version of LDOS, double sided support was undocumented, > because Tandy didn't sell a double sided drive, until the model 4D?) I know it will work. > Remember that the PC uses all drives jumpered as if they were :1/DS1/B: Right. I well remember how to jumper drive selects. > Radio Shack used an "unused" pin of the interface for drive :3/DS3/D:, > Unfortunately, that was the pin that was "reserved" for side select! > That poses a problem for model 1 (with four drives on one cable), but not > for III, 4, nor 4P Yes. I was reading about that the other day. I don't have any 4-drive units, just multiple dual-drive units. > If you have a model 1 drive that has the modification for drive select using > the side select signal, don't use it if you use any double sided drives in > the machine, or clip that wire on the drive. Good to keep in mind. I borrowed a half-height "Bachelor" FD-104 from a Model 1 for drive/controller testing. I cannot find docs for it, and barely a mention, even in TheRef. There is one jumper block by the 34-pin edge connector - marked D.S. / 0 / (1) / 2 / 3 / MX. (the '1' is damaged/missing because of a PCB via). It seems the first jumper is likely to be single/double-sided (there are 2 heads), then 4 drive selects, then the MX one-drive-only-select jumper. > You can use "half-height" drives in a model 3 or 4. Yes but at the moment, I only have one half-height 40-track drive, that Bachelor FD-104. My only loose drives are 80-track HD units. -ethan
