On Wed, 15 Jun 2005, billdeg wrote:
> Hi - I am a relative newbie to the TRS 80 Model 4 world. I am
> seeking basic instructions for hooking up an external to trs 80 model
> 4...For example, do you attach a cable to the external drive port on
> the model 4 like a regular external disk? I cannot find any
> documentation (yet) that takes a person through the hardware
> installation and testing. I have some harddrives but I am unsure if
> they work and/or are configured to be receptive to the Model 4.
My second machine was a Model 4, but I was never able to afford a hard
drive for it. I can answer a couple of your questions, though. The Model
4 does not have an internal hard drive controller: you have to hook up an
external "primary" hard drive unit which has the controller installed. It
connects to the system via a long ribbon cable to the IO bus connector on
the bottom of the machine. Additional "secondary" hard drives may be
connected to the primary. The drive itself was "hacked" onto the
controller, to get the write protect circuitry to work. The drive
...has a pushbutton switch to enable/disable write protect, which
required connection directly to the drive electronics. A document which
tells you how to install different drives in the housing is here:
The same site has a lot of hardware mod info:
> Should Montezuma cp/m automatically detect the external hd or is
> there a program you'd need to run? does montezuma cp/m have
> harddrive support utilities? I have a number of versions of DOS's
> including Montezuma cp/m 2.2, but I am unsure which is best. I also
> have some ROMS that I can install into the Model 4 to automatically
> boot to the hard drive, but I don't want to move too
> quickly...looking for advice and doing research first. I will keep
> looking on this end.
Montezuma Micro was my favorite CP/M for the Model 4, because it could
read/write just about any CP/M formatted diskette around. It did not have
hard disk support built in, but they offered a driver for it:
It's in disk image format, so you can fire up Tim Mann's xtrs emulator:
or David Keil's Model III/4 emulator for Windows:
and create a diskette for your Model 4.
> I have a Percom 5MB external disk drive that's my first candidate for
> the Model 4, but I have a few others to try as well. If there is a
> particular model(s) that's favored, please advise. I don't have any
> Tandy brand external drives.
The 5Mb primary drive in the picture is mine, but I believe the
controller is defective. I've tried another drive in it (after rewiring)
and it still doesn't work. I'd love to get a working drive on my Model 4.
Mike Loewen mloewen@...
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