Tim Mann's TRS-80 Pages

 Business card from 1981

LDOS and Me

In a previous life, I used to be an operating system programmer for the Radio Shack TRS-80 Model I and Model III. No, I didn't work for Radio Shack. I worked indirectly for Logical Systems, the company that produced LDOS and (later, after I left) Model 4 TRSDOS.

In 1980-81 when I worked there, Logical Systems was a new joint venture, just getting started. The principals were Misosys (Roy Soltoff's company, in Alexandria, VA), Galactic Software Ltd. (Bill Schroeder's company, in Mequon, WI), and Lobo Drives (in Goleta, CA, near Santa Barbara). The name was chosen because Logical starts with an "L," providing an alternative explanation for the name "LDOS," which originally stood for "Lobo Drives Operating System."

LDOS evolved from an operating system called VTOS 4.0, which was written by Randy Cook, the same programmer who wrote the original Model I TRSDOS (up through version 2.1) for Tandy. Lobo couldn't use Model I TRSDOS on their hardware, because they were selling an improved disk interface of their own design (the LX-80) that was not hardware compatible with Radio Shack's disk interface. VTOS had a second boot sector and additional code that enabled it to boot and run on both platforms, and was quite a bit more advanced than TRSDOS.

Lobo had a falling out with Randy Cook, the details of which I wasn't privy to, and they hired Galactic and Misosys to work on fixing bugs in VTOS. They were unable to obtain the source code, so all the work was based on the raw machine code. Fortunately Roy had an excellent disassembler! The project soon expanded from an effort to fix up VTOS for use by LX-80 owners into a joint venture to produce a new version of the operating system, called LDOS, for sale to the TRS-80 public at large. I understand that Randy was paid for rights to his work, and he was acknowledged in the LDOS manual, but again I wasn't involved with the agreement and wasn't told the details. I was never fortunate enough to meet Randy.

I got involved shortly after this process began. I was finishing college at the time. Just for fun I had been disassembling a copy of VTOS 4.0 that I had bought directly from Virtual Technology, Randy Cook's company. I found a number of bugs and started posting fixes on CompuServe, then a very new service. Eventually Dennis Brent, the main distributor of VTOS, issued an updated release with patches and some extra utilities from me and a few other folks. Dennis generously sent me an unsolicited royalty check and provided many words of encouragement.

Bill Schroeder soon found out about my work on patching VTOS and offered me a job with Galactic to work on LDOS. Conveniently, I lived in Milwaukee, just a few miles south of Mequon. After I came on board, there were five of us working on the system, four at Galactic (Bill, me, Chuck Jensen, and Dick Konop) and one at Misosys (Roy). We all did a mix of design, programming, debugging, documentation writing, writing for the LDOS Quarterly, phone support, and CompuServe bulletin board support, in varying proportions. Roy was the lead designer and programmer, while I probably had the second-largest role in those areas for the relatively short time I was there. I worked only on LDOS, while the others all had other Galactic or Misosys products to support as well.

I remember contributing PR/FLT, the Model III RS232 driver, parts of the Model I Doubler driver, extensions to Basic, a rewrite of the LX-80 ROM, CONV/CMD, bits of documentation, LDOS Quarterly articles, and many bug fixes. I gained a very thorough knowledge of Model I and III hardware, including such variants as the Percom and Radio Shack double density adaptors for the Model I, as well as the LX-80. I ended up replacing my Radio Shack Expansion Interface with an LX-80.

Our work resulted in an excellent operating system for stock Radio Shack hardware as well as Lobo hardware, and we soon started porting LDOS to the Radio Shack Model III as well. Unlike Radio Shack's Model I and III TRSDOS, LDOS provided full media interchangeability between Model I and III, allowed application programs to be easily written or patched to run on both systems, and supported hard drives.

While I was still there, Bill persuaded Tandy to license LDOS as its official hard drive operating system. This was quite a coup for our tiny company. Later Logical Systems was selected to do TRSDOS 6 for the Model 4. Roy and the rest of the team started with the LDOS 5 code base, so I'm sure that some of my code survived.

I left after less than a year (in September '81) to work on a Ph.D. in computer science at Stanford. I still did some consulting for Logical Systems on the side for a year or two. Ironically, my first job after finishing my Ph.D. six years later paid less than Bill had been offering me to stay at Logical Systems in 1981. On the other hand, the company was nearly dead by 1987; they failed to find a new direction as Z-80 systems became outmoded. Eventually Misosys bought Logical Systems (which had earlier bought out Galactic), and Bill got out of the microcomputer business. A few years later Roy folded Misosys and got out of the business himself.

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