The TRS-80 Model II

TRS-80 Model II (without floppy drive)

My Model II. The floppy drive has been removed for repairs.

The first computer I owned was a TRS-80 Model I. A great deal of pages have been written about this machine, no need for me to add another one. Later Tandy introduced the Models III and 4, wonderful machines you could upgrade to if your Model I gave up the ghost. But what always intrigued me was the "missing link", the TRS-80 Model II. There were impressive stories (and prices) about it in the Tandy catalog, but nobody I knew owned one. Years later, when my "fame" as a computer collector had spread around, I finally got a call from someone who wanted to get rid of a Model II. Bingo!

Information on the TRS-80 Model II

The inside of a Model II

Inside of Model II. Computer card cage on the left, monitor circuit and power supply on the right.

Model II system description

The Model II is a computer system that was manufactured in the USA by Tandy between ~1980 and ~1984. It is a large cabinet which holds the computer, the monitor and a single sided full height Shugart 8 inch drive, which used single sided floppies with a capacity of 500K. (That was an enormous amount compared to the ~87K that was free on a Model I TRSDOS system disk.) The computer itself is on a number of cards in a passive backplane. The processor is a 4 MHz Z80A. The system has a complete Z80 chipset, the PIO, SIO, DMA and CTC are all there. It has 64K RAM and a ROM that can be bank switched away, ideal to run CP/M. There are two serial ports and one parallel. The display is 80x24. Three extra 8 inch drives can be connected, so you could have 2MB disk space online. Later there even was a 8 meg external hard disk available.

You got TRSDOS and BASIC with the system, and an impressive set of manuals with detailed descriptions of the DOS and BASIC commands, and even detailed descriptions of the DOS service calls you could use in machine code programs. To top it off you also got the technical hardware manual with all the schematics of the computer and monitor, and a service manual of the disk drive. Options for the machine included a hard disk controller, an arcnet network card, a graphics card and a 6 MHz 68000 board set with extra memory (up to 512K) so it could run XENIX.

The Model 16

The Model 16 (1983)

Later there appeared extra members of the Model II family that were compatible:

The Tandon slimline drives used in the later models were different from the old Shugart full-size ones, they were double sided and could hold 1.2MB. They had a faster step rate which speeded up disk access. They used low voltage motors to rotate the floppy, so were less noisy and ran only when there was disk access instead of all the time like the old drives did. Unfortunately they were less reliable.

The Model 12

The Model 12 (1984)

The Model 12 and Model 16B had a new keyboard and a white cabinet, instead of the dark grey other ones, a bit like a giant Model 4. The Model II had a white screen, all the others a green one.

There were several operating systems for the Model II range:

The Model 16B

Benson Chow's Model 16B with internal hard disk (1984)

The Model 16 came with TRSDOS-II, TRSDOS-16 and a 68000 machine code editor/assembler. If you ran XENIX you could attach two terminals (of course you used the TRS-80 DT-1 terminal) to the system for a total of three working positions. If you were very careful with the external hard disk, especially with the power up and power down sequences, the system was reliable.

The Tandy 6000 had a better designed 68000 board that ran at 8 MHz and a faster hard disk, so its total speed was much faster than the Model 16 and 16B.

Row of Model II manuals

Row of Model II/16 software

Tandy had a great deal of software for the Model II. In the DOS itself was a communications program. There was an advanced version of their strange Scripsit word processor, that had the posibility of outputting documents to the serial port for transfering to other systems. The well known Visicalc was available (and it could use extra memory cards for very big spreadsheets) as well as the Profile Plus database program. The programming languages COBOL, FORTRAN and compiled BASIC were available, as well as a great macro assembler. There even were very specific programs, like Ligitation Support for lawyers, Job Costing for architects, ReFormatter to exchange disks with IBM mainframes, Financial software etc etc. The list is very long.

Unfortunately there was not much support for the system from firms other than Tandy. There was a thin bimonthly magazine, the Twelve/Sixteen, and the 80 Micro magazine had a Model II/12/16 column, and with every BASIC program it published there was a list of changes needed to get it to work on the Model II. RACET Computes sold a number of utilities for the Model II, so you had almost all the features of NewDOS/80 added to the Model II DOS. There were Superzap, a disk editor, a fast single pass assembler, a disassembler, extensions to the BASIC language, etc. It was a great package.


But fortunately there was CP/M for the Model II. I have two. One was made by FMG corporation, version 2.21. It ran every CP/M program I tried. Tandy had a CP/M Plus for the Model II, 12 and 16, available in the original Digital Research binders, with the TRS-80 logo added to them! It supported hard disks in the TRSDOS format. It could read Pickles and Trout CP/M double density disks. You got four diskettes. CP/M plus boot disk banked, boot disk unbanked, utilities disk and TRSDOS floppy conversion disk.

For CP/M there was the IMP communications program, which had an extension for the serial ports on the Model II. It was quite fast.

The Model II and its siblings were a fast enough and flexible machine with a great deal of software available for it. They could do things that were impossible with most other systems available at their time. Unfortunately it was very expensive and very noisy.

System disks

It is hard to make system disks for the Model II available for download, since the Model II uses 8 inch drives. But finally there is a solution. If you build a cable to connect a HD 5.25i drive to the Model II, it is possible to use 5.25 floppies with the machine, and you can use the Teledisk program to create copies of system disks on 5.25 floppies. As a test I built a cable per the instructions on Frank Durda's page and I created an image of a CP/M disk for the Model II CPM-MII.TD0.

The PSKI Model II archive has more disk images of Model II disks.

TRS-80 Model II Links

Thanks to Benson, xdm at for proofreading and correcting this page.

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