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Overview

Operating Systems

TRSDOS
NEWDOS
MULTIDOS
DOSPLUS
LDOS

Emulators
Internals
Hardware


Model 3

Model 3 Overview

The Model 3 was Tandy's second personal computer. One of the reasons it was developed was because the FCC instituted regulations about the RF emissions generated by computers (and other electronic devices). The Model 1 was completely unshielded (a fact many owners who also like TV and/or radio discovered the hard way), and was unable to pass the emission restrictions.

The Model 3 was somewhat better for new users because the monitor and keyboard were all in one unit. That got rid of the problems the Model 1 had with funky connections between the keyboard and expansion interface. The serial port was also usable. :-) The cassette interface supported both the 500 baud speed of the Model 1, as well as a much faster 1500 baud. Using a cassette based system was much less painful with the data screaming along at that speed.

The Model 3's BASIC ROM was 2k larger (at 14k) than the Model 1, added the 1500 baud cassette speed, allowed for left and right shift keys to be at separate addresses in the keyboard memory area, and added a 25 or 30 HZ real time clock routine (country dependent) which allowed for TIME$ to be added to ROM BASIC.

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Model 3 Operating Systems

As in the case of the Model 1, there were quite a few different disk operating systems available for the TRS-80 Model 3.

Below, the major operating systems for the TRS-80 Model 3 are listed, along with some comments from myself and others.

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TRSDOS

In MY opinion, the Model 3s TRSDOS was its one unredeeming quality. Thank goodness for LDOS, NEWDOS/80 and DOSPLUS, and whatever other third-party operating systems were available.

Instead of keeping things as compatible as possible with the Model 1, Tandy decided to use a different directory track layout. Also, the directory records were extended to be 48 bytes long, instead of 32. They supplied a CONVERT utility which would copy files from a TRSDOS 2.3 disk to a TRSDOS 1.3 disk, (why was Model 3 TRSDOS at a lower version number, anyway?), but it had a few problems when files on the Model 1 disk were password protected.

In contrast, most (or all) of the other operating system vendors made sure that their Model 3 systems could read disks from their Model 1 versions without any trouble.

Eventually there will be a link here with more Model 3 TRSDOS information.

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NEWDOS and NEWDOS/80

Apparat made NewDos/80. This was much more powerful than their first release of NewDos 2.1 for the Model 1. NewDos/80 could do just about anything, and did it rather well.

If you would like to see it, there is a page of NewDos/80 Commands that gives a rundown of the commands available on both the Model 1 and Model 3 versions of NewDos/80. Thanks to Sander Berents, who sent it to me. All I had to do was convert it from LaTeX format to HTML.

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DOSPLUS

Micro Systems Software made DOSPlus for the Model 3. I think most of the Model 1 comments apply.

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MULTIDOS

Again, the Model 1 comments probably apply to the Model 3 version. I really need more MultiDos information.

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LDOS

Logical Systems wrote LDOS for the Model 3. Tandy even sold it as their Model 3 Hard Disk Operating System, since TRSDOS was unable to support those. For the most part, all the comments in the Model 1 section of the page apply to the Model 3 version.

If you're interested, here is another link to that page full of LDOS Internals. This has lots of good programming information for both the Model 1 and Model 3 versions of LDOS. The entire LDOS 5.x manual is available on the web at Tim Mann's TRS-80 page, along with disk images of LDOS 5.3.1 for the Model 3 (and Model 1). These have been released by Roy Soltoff, who holds the copyright on them, as freely available. See Tim's page for the full details.

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Model 3 Internals

In order to keep the size down a little, these are separate pages.

Here is a page of Model 3 (and 4) I/O Ports

Here is a page of Model 3 (and 1) RAM addresses

Here is a page of Model 3 (and 1) ROM addresses

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Other hardware and stuff

This is still being worked on. There were a number of hardware additions you could make to the Model 3, most notably a hard disk controller and hard disks.

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The TRS-80 Home Page created and maintained by Pete Cervasio
cervasio@airmail.net

Copyright © 1998 Pete Cervasio