TRS-80 Model 4 help requested

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Feb 26 18:14:01 2003

> Hi pat,
>
> I too just picked up a model 4. I didn't get any disks but mine
> says "Disk?" when I power it up. I opened it up and mine is a basic 64k
> machine with two SS disk drives. The drives in mine are made by Texas
> (somebody), Texas Peripherals maybe? I checked and they're 40 track SS

The Texas Peripherals drives are _exact_ copies of Tandon drives (same
schematics, same PCB layouts, same mechanical bits. I've swapped
mechanical parts between Texas Peripherals and Tandon drives, and I use
the repair info in the M3 manual for Tandon drives too...

They almost certainly are the origianl drives. Or at least Texas
Peripheral drives were used by Radio Shack...

> drives. I believe these are the original disk drives for the M4 but I've
> been told that they will support 80 track and DS drives. But I don't
> know if you had to patch the BIOS and/or OS to do that.

The bootstrap ROM (there's no real ROM BIOS in these machines) expects to
boot from a single-sided disk in a 40 cylinder drive. Most people kept
drive 0 as a 40 cylinder unit for this reason.

To use DS or 80 cylinder drives you have type a couple of commands if
you're using a sensible OS like TRS-DOS 6 (== LSDOS). If you're running
one of the M3 OSes, then you might have to patch things....

-tony
Received on Wed Feb 26 2003 - 18:14:01 GMT