Exploring 1984 OS-9 on a 64K TRS-80 Color Computer – part 1

See also: part 1, part 2 and part 3.

NOTE: The images in this article were taken from the excellent Radio Shack Catalogs archive website: https://www.radioshackcatalogs.com/

1984 was a big year for home computers. Not only was the Apple Macintosh released with that famous 1984 Superbowl ad, but Microware’s OS-9 operating system made a debut at Radio Shack.

Des Moines-based Microware had created a product called RT/68 for the Motorola 6800 processor. It was advertised in the February 1977 issue of Byte Magazine:

This led to them working for/with Motorola to create a high performance BASIC programming language for the Motorola 6809 processor. This led to them creating an operating system to support it. That operating system was called OS-9. (I assume the 9 was chosen because of the 6809 processor.)

I do not know the details of how it happened, but at some point Tandy/Radio Shack and Microware decided to bring out a version of OS-9 for the Radio Shack TRS-80 Color Computer. It was introduced in the 1984 Radio Shack catalogs, along with a 64K version of the Color Computer that was needed to run it. (OS-9 required 64K on the CoCo, but OS-9 itself could be embedded in ROM to run on industrial equipment with as little as 4K RAM.)

OS-9 was listed in the 1984 Radio Shack catalog, as well as the two 1984 Radio Shack Computer catalogs (RSC-10 and RSC-11):

Here is how the 64K version of the Color Computer was presented in the 1984 catalog:

And this is a how OS-9 was described in the short entry of the 1984 catalog:

At the time, I remember my Radio Shack salesman telling me OS-9 was needed to make full use of the 64K in my Color Computer. The Microsoft BASIC ROMs in the CoCo were limited to using less than 32K, regardless of if you had more than that installed in your machine.

The computer catalog went in to more details on both the machine and the operating system:

New 64K CoCo in the OS-9 in the Radio Shack Computer Catalog RSC-10
OS-9 in the Radio Shack Computer Catalog RSC-10

I found it interesting that the same entry appeared in the second1984 computer catalog (RSC-11), but without the color. (I did not go through it word-for-word to see if there were any text changes, so let me know if I missed something.)

Radio Shack Computer Catalog RSC-11

Humble beginnings! Over the next few years, CoCo OS-9 offerings would continue to grow, adding compilers like C, and eventually a more advanced OS-9 Level 2 for the CoCo 3 with an optional mouse-driven GUI.

But in 1984, there was far less you could actually do with OS-9 except write programs for it in either 6809 assembly (notice the assembler was included) or the sold-separately BASIC-09. (It was actually just “BASIC09” in the documentation, without the dash.)

I thought it might be fun to boot up this original version of CoCo OS-9 and see what all it could do.

To be continued…

8 thoughts on “Exploring 1984 OS-9 on a 64K TRS-80 Color Computer – part 1

    1. Allen Huffman Post author

      On a CoCo 1, 32K of OS-9 could be put in to ROM and have 32K available, pretty easily I bet. Getting access to the full 64K of RAM would be tricky, since there is no memory management unit on the CoCo 1/2 systems. But drive code could use the other 32K as a RAM drive, I bet.

  1. Rogelio Perea II

    Personally I find working with Level 1 more rewarding than Level 2, the later is just tasty gravy on the CoCo 3. Currently trying to port DECB PMODE4 graphics programs to BASIC09 under Level 1, an interesting learning experience; the holy grail of my projects to incorporate the DRAW facility found in Level 2’s GFX2 into Level 1’s GFX module…

  2. L.+Curtis+Boyle

    The 64K Coco and OS-9 were the cover story for the September 1983 Rainbow, so they came out in late 1983 (first showing up in the 1984 Radio Shack catalog). A little bit earlier. :)


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