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Ian Blythe's Homepage
This is my first draft of the history of FLEX and goes back to the beginning to give the rationale for FLEX. If you can contribute any further information to this, please send your info or comments to me by e-mail to f_u_g@ipblythe.com (remove underlines).

The history of TSC FLEX goes way back to the mid-1970s and to the first introduction of Personal Computing. It's well known that the Altair MITS 8800 was the first personal computer, as announced as a kit in the December 1974 edition of Popular Electronics for US$439. However most people have forgotten that SouthWest Technical Products (SWTP) produced a kit for a computer based on the new Motorola 6800 and introducing the SS50 50-pin bus not long after in July 1975. This computer proved more popular than the MITS 8800 as the SWTP computer had a basic Operating System in PROM (Programmable Read-Only Memory) (you had to toggle data into the MITS every time you used it). Unfortunately SWTP was swamped with the popularity of their kits and many people experienced delays in getting their kit.
(Altair also introduced a 6800 version of their computer, but it proved too expensive and so did not last long)
These were the days when we wrote programs by hand and punched paper tapes to enter our program through our ASR Model 33 Teletypes, so having the PROM saved a lot of time. Audio cassette tapes were also adapted for program storage (remember the Kansas City and Tarbell standards anyone?).
The SWTP computer provided a Cassette tape interface, athough it was widely acknowledged to being very slow to load at 300 baud (taking over 15 minutes to load the famous 8K Cassette Basic interpreter by Robert Uiterwyk).

PERCOM introduced the first 5.25 inch Disk Drive for the SWTP SS50 bus and the first 6800 Disk Operating System (DOS): MINIDOS. This was a very rudimentary, but solid, DOS and used single-sided, single-density hard sectored disks holding a wonderful 85K of data. (35 tracks with 34 user tracks, 10 sectors per track (each of 256 bytes, with 4 taken by the DOS). The PERCOM kit of two drives, power supply plus controller package was $1000. Hard sectored disks had a series of holes in the center of the hub of the floppy disk, each hole indicating the start of a sector. Soon though, soft sectored disks, where the sectors were indicated by the data on the disk, became more popular as higher disk capacities could be achieved. Percom was owned by Harold Mauch, who sadly died of leukemia with Percom disappearing soon afterwards.
Microcomputer Systems introduced the first Mini-Floppy (5.25") interface for the new $600 Shugart drives.

The owner of SWTP, Dan Meyer, met Dave Shirk, the owner of Technical Systems Consultants (TSC), around the time of the introduction of the soft-sectored mini-floppy and they became good friends. TSC in 1976 consisted of Dan, Don Kinzer, and a secretary. In spring 1977 Don Kinzer left and Dan Vanada became the company vice-president. Rich Kovarik also joined TSC at that time becoming secretary and treasurer. TSC ran its first advertisment in the August 1975 edition of Byte magazine.
TSC wrote a DOS for the new drives and called the DOS MiniFLEX. Version 1.0 was introduced in 1976. MiniFlex was superceded by FLEX 1.0 for the 6800 4 months later. This caused a few problems at the time as the disk format was different between MiniFLEX and FLEX, however soon everyone was using FLEX. Support for MiniFLEX was stopped by TSC in November 1979, however, by this time FLEX was supporting 8" and 5.25" drives for the 6800, and then, after Motorola introduced the MC6809, the SS50 bus was modified for the 6809 and FLEX 9 for the 6809 was born.

Users found that it was possible to add a switch to the SS50 system to allow both 6800 and 6809 processor cards to be used. It was also possible to write programs for both 6800 and 6809 systems as TSC arranged the system DOS call locations to be at $A000+ for 6800 FLEX, and at $C000+ for 6809 FLEX, so a simple assembler switch could provide a program for both systems. An interesting relic of the original single density disks, which became the first standard for software distribution, caused the new double density disks to be formatted with track 0 in single density. This was so single density systems could determine that the disks were in the FLEX format, but not suitable for the DOS.

Ronald Anderson began a newletter for the MiniFlex User Group. Don Williams, editor of 68 micro Journal, invited Ron to join, MiniFLEX User group users became automatic subscribers to 68Micro for the length of their subscription to Ron's newsletter. The most remarkable thing about TSC FLEX is how it became to be adopted by virtually all the makers of 68xx SS50-based computers (and even for the Tandy Color Computer and UK Dragon), and for the amazing amount of software that was written for FLEX. This software covered not only Assemblers and Basic Interpreters, but also cross assemblers and cross compilers, Database managers, debugging tools, several FORTH language implementations, editions of 'C' and Pascal and the famous PL/9 programming language, spreadsheets, text editors and processors, word processors and spelling checkers. In fact, most of the tools that we take for granted now on our PC/Mac/unix machines today. Remember too that FLEX used only 8K of memory and provided up to 48K of user memory!

TSC, having produced many high quality programs for 6809 FLEX, went on to produce a unix-like multi-user system for the 6809, UniFLEX. Unfortunately the timing of the introduction of UniFLEX came at the same time as the arrival of 16-bit processors and then the ubiquitous PC. UniFLEX was sold to an investor and then faded away, TSC closed down, SWTP became too successful in its time and suffered the consequences.
And so it is now up to us, the FLEX User Group, to fly the flag for one of the most successful, and yet forgotten, Disk Operating Systems of the early era of personal computing.


Copyright © 1998-2001 Ian P. Blythe on behalf of the FLEX User Group
Mailto: f_u_g@ipblythe.com (remove underlines from e-mail address - Say NO to UCE)