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Differences between model 1, 3 and 4

Abmvk

Experienced Member
Joined
Feb 11, 2023
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88
Location
Netherlands
I am searching online, but most I find is rather high level. I am looking for details, as much as possible. For example, I just found out that the disk basic of the model 1 has the SET and RESET command, but the disc basic of the model 4 does not. And (my) model 4 has no BASIC in ROM, where the model 1 does.

But well, really any source of detailed comparisons would be appreciated!
 
I suspect the best resource would be to just look at the Radio Shack catalogs back in the day.

 
And (my) model 4 has no BASIC in ROM, where the model 1 does.

Do you have a Model 4P? Regular desktop Model 4s have Model III basic in ROM, just hold down the BREAK key when you turn it on. (Or boot a Model III DOS.)

Short version of the response to this question: a Model 4 booted into a Model 4 DOS is a *completely* different computer from the Model I and III. (Those two are mostly alike.)
 
I have a model 4, not the portable, as far as I can determine. And it doesn't boot to Basic, even when I hold down the BREAK key. At least, I don't think so. Minutes after my initial post the computer was producing white smoke, so there is some repairing to do first.
 
That was likely the Square RIFA Cap(s) blowing on the Power Supply.
They should be replaced ASAP.

If it's a TANDY Power Supply versus ASTEC, you need to remove it and check the
Row of Pins for little rings around each pin. Then re-flow the solder for each pin with
some KESTER 63/37 Solder. That will fix the Tandy Power Supply.


Larry
 
All Model 4's except the portable 4P have BASIC in ROM. If your Model 4 wasn't going into ROM BASIC when you hold down the BREAK key on boot there are only a few possibilities.
  • You actually have a 4P (if the diskettes are oriented vertically it's a 4P). Or show us a picture.
  • The BREAK key is broken.
  • You didn't hold down the BREAK key before powering on or resetting the machine.
  • Something quite unusual is going on.
The Model 4 wikipedia page shows the difference between the models pretty well:
https://en.wikipedia.org/wiki/TRS-80_Model_4
 
This wikipedia page has a good overview of changes from Model 1 to 3

Apart from the obvious form factor change and other functional improvements, the main differences from a hardware perspective (IMHO) were the move memory mapped IO (e.g. Disk Controller) from $37Ex into IO address space, which made way for an expanded 14KB ROM. If you search there are many sources of the memory and IO maps, which can be compared. I think this was the biggest areas of incompatibility requiring minor software changes.
 
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