Imaging TRS-80/III single-sided disks

Fred Cisin cisin at
Thu Jun 25 19:19:08 CDT 2015

A few more gotchas to be aware of:

Some of the operating systems on TRS-80 started the sector numbering at 0. 
Therefore, depending on which operating systems were used, you could have 
sectors numbered 0 - 17 , or 1 - 18.   That can be confusing if your PC 
can't read the first sector, but tells you that it successfully read 
sector #1.

Model 1 TRS-DOS is SINGLE DENSITY.  IMD can handle that IFF the FDC in 
your PC is one of the ones that supports FM/SD.   NOTE: some/many? TRS-80 
users installed additional hardware for double density, but the OS might 
still require FM/SD for track 0.   Disks written on a stock model 3 for 
use in a model 1 are not quite the same format as model 1 disks.

Model 1 TRS-DOS uses some "NON-STANDARD" DAMs (Data Address Marks).  I 
don't know how to read those with PC FDC.  But, they can be read with 
Catweasel, OptionBoard, or other "flux transition" boards.
Or design and build a PC FDC board with a 1771 WD FDC and a WD 179x FDC 
just to be able to handle disks with NEC/WD incompatabilities - NOTE: that 
disk controller should ALSO have an NEC FDC, or you won't be able to have 
full PC compatability.

Model 1 TRS-80 has 35 tracks.  They started off using the Shugart SA-400 
floppy drive, which is 35 track.  I think that most/all? of their later 
drives could do a full 40 tracks, BUT don't count on the software 
supporting that.  Expect 35 tracks for TRS-DOS, although most/all? of the 
after-market operating systems supported 40 track, and some supported 
double sided drives ("Gee, didn't expect THAT!"), and some users even used 
80 cylinder drives, for 720K capacity.  Yes, there were also hardware mods 
for TRS-80 to use 8" disks.  Yes, you can put 3", 3.25", or 3.5" drives on 
a TRS-80.

Not all TRS-80 diskettes were of the highest quality.  Be prepared to 
clean the heads of your drive after you finish, and maybe periodically 
part way through.  Some TRS-80 users considered Wabash to be "premium" 

Grumpy Ol' Fred     		cisin at

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