The TRS-80 Journey Continues

Fred Cisin cisin at
Thu May 5 17:53:39 CDT 2022

>> The Teac FD-55GFR is a 96tpi drive.  It can replace a 55G (1.2M), or a 55F 
>> (720K) depending on controller, but it still has a narrow head for doing 80 
>> tracks.   It will have to be jumpered to run at 300RPM, not 360.

On Thu, 5 May 2022, Bill Gunshannon via cctalk wrote:
> It has a jumper that leave that up to the controller.

But, the TRS-80 controller doesn't implement that signal; if the default 
of signal not present is 300 RPM, then it's all set, . . .

> I used double sided as far back as my first Model III.  Even had a
> full height Tandon 80 track double sided drive.  All I ever needed
> was DOSPLUS or NEWDOS80.
That would be the Tandon TM100-4

Although TRS-DOS didn't (until 6.0?, when TRS-DOS became rebranded LDOS), 
the after-market OS's supported DS and 80 track.
I don't remember how you needed to tell the OS that you had DS or 80 

But, once the OS knows, then the 55GFR, operating as a 55F, can, of 
course work.
Do you know how to tell your CP/M about DS and 80 track?

>> Discusses the drive selects and Mentions that you can use 55GFR, but 
>> doesn't give the details that you need  (300/360 RPM, double stepping, 
>> etc.)

> The 4P has the missing pins.  I never liked it and usually end out
> putting in real cables and using Drive Select like it was intended.
> At least until IBM won and the started making 3.5" drives without
> any way to do drive select.

Good.    The TRS-80 and IBM special cables were specifically because they 
didn't think that their own staff, and customers, could set drive-select 
properly on the drives.

>> But, more importantly, is the fault ONLY when format/verify?
>> Does it still READ disks that you already have?
> Haven't really tried that.  Most of the disks I have are over
> 20 years old.  If it fails to read who's fault is it?  The drive
> or the disk.

But, if it WORKS, . . .

>> One more possibility to pay attention, (you probably already know this, so 
>> sorry if saying it offends you), ...
>> You need to use 300 Oerstedt ("360K") diskettes.  If you use 600 Oersted 
>> (1.2M) disks, they will seem to work, and then immediately, or VERY soon, 
>> lose their content.
> Yeah, I knew about that.  I still have piles of real floppies laying
> around.  :-)

The college purchasing agent was in bed with a supplier, and kept getting 
us Roytype HIGH DENSITY disks for our TRS-80 lab.  Even when we explicitly 
said not to substitute.

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