The Exatron Stringy Floppy

written by Matthew Reed

Exatron advertisement

Exatron advertisement from the January 1980 issue of 80 Microcomputing

There were quite a few different storage products available back in the early days of the TRS-80 Model I. In the long term, the floppy drive (and later the hard drive) completely beat out all of the competition. But back when floppy drives were considered too expensive by many, one of the most popular storage products for the TRS-80 was the Exatron Stringy Floppy.

Founded in 1974 by Robert Howell, Exatron was a supplier of automated test equipment for manufacturers and OEMs. Exatron first demonstrated the S-100 version of the Stringy Floppy at the West Coast Computer Faire in March 1978. The TRS-80 version was introduced in May 1979 at the San Francisco Computer Faire. An early price for a TRS-80 starter kit (Stringy Floppy, wafers, and software) was $299.50. The Stringy Floppy provided an additional cost savings over floppy drives because it didn’t require an Expansion Interface. By 1982, the price for a single Stringy Floppy drive had come down to $99.50.

The Stringy Floppy was the only storage device other than floppy drives to achieve a degree of software support. Many programs, including games, were available on Stringy Floppy wafers. Some programs, such as Electric Pencil, had special Stringy Floppy versions. Jim Perry and later Spencer Hall wrote “@NEWS,” a column about the Stringy Floppy that ran in 80-U.S. Journal from the March/April 1980 issue to the January 1983 issue.

Exatron advertisement

Exatron advertisement from the August 1981 issue of 80 Microcomputing

The Stringy Floppy transferred data at 7200 bits per second, over 14 times as fast as a Model I cassette. At that speed, a 16K file only took 24 seconds to load. The Stringy Floppy had the additional advantage over cassettes that the continuous loop wafers never needed to be rewound or positioned. The wafers were packaged in lengths which varied from 5 feet to 75 feet, with the wafer length determined the amount of storage. For instance, a 20 foot wafer could store 16K and a 50 foot wafer could store 48K.


Installing the Stringy Floppy on a Model I was as simple as plugging the unit directly into the Model I I/O bus. The Stringy Floppy routines were activated by typing:


and then:


I suspect that most Stringy Floppy users remember that sequence even today. The Stringy Floppy routines also debounced the Model I keyboard, although that useful feature was never really advertised.

The Stringy Floppy ROM occupied a 2K hole above the Level II BASIC ROM in the Model I memory map. Li-Chen Wang, who wrote the Tiny BASIC which served as the basic for the Level I ROM, also wrote the Stringy Floppy ROM.

Exatron advertisement

Exatron advertisement from the November 1982 issue of 80 Micro

The Model III had no equivalent hole in its memory map, so a more roundabout method had to be used. The Model III Stringy Floppy also had a cassette tape connection and could emulate a cassette recorder. The Stringy Floppy routines could be loaded into the upper 4K of memory using a special wafer. The commands used were similar:


and then:


The special wafer could then be replaced and the Stringy Floppy would otherwise work just like it would on a Model I.


The Stringy Floppy was controlled entirely through BASIC commands. The commands were prefixed by an @ symbol, and included @LOAD and @SAVE, which saved and loaded BASIC programs. The @SAVE command could also save machine language programs. Programs stored by the Stringy Floppy were numbered and multiple programs could be saved on one wafer. Up to seven Stringy Floppy units could be connected at one time, so the unit number could be specified in the commands.

The best description of how the Stringy Floppy worked I ever saw was contained in an Exatron advertisement:

The ESF uses a miniature tape cartridge (called a “wafer”) as a data storage medium, about the size of a business card and 3/16th of an inch thick. The tape used inside the wafer is a special Mylar based Chrome Dioxide type, specially developed for digital applications. Wafers are available in several lengths, 5 feet being the smallest and capable of holding up to 4 thousand bytes of information – the 75-foot wafer is the largest available and can hold up to 64 thousand bytes of data. The wafers contain a single reel of the special tape connected as a continuous loop, the ends being spliced together with a piece of reflective tape. In operation the ESF drive unit pulls the tape from the center of the reel inside the wafer, causing the entire reel to rotate. Thus, the tape automatically winds itself around the outside of the reel at the same rate at which it is pulled from the center. This process is similar to that found in an 8-track cartridge.

A&J Micro Drive advertisement

A&J Micro Drive advertisement from the April 1984 issue of 80 Micro


In 1983 as part of a reorganization, Exatron announced that it was changing its name to Entrepo (which means “storage” in French) and focusing on the many home computer companies that were interested in a low-cost storage device. It also shut down its mail-order business, although promising not to forget the estimated 5,000 to 10,000 TRS-80 Stringy Floppy owners.

At that time, Jim Howell, son of the Exatron founder, took over the mail-order Stringy Floppy business with his company, A&J Micro Drive. In addition to the Model I Stringy Floppy, A&J Micro Drive also sold a type of Stringy Floppy drive for the Model 100. It continued to advertise drives well into 1986.

The Exatron company stopped manufacturing the Stringy Floppy many years ago, but is still a prominent manufacturer of test equipment and one of the few major TRS-80 companies that still exists today.

Categories: Hardware


Clark Calkins says:

I just stumbled on your site and it brought back many fond memories. I worked for many years with Bob Howell at Exatron on their Stringgy Floppy. I worked on a Digital Group interface initially and then on a Timex version. A the time I was an assembly programmer and wrote lots of code for this little device. For the Timex, I wrote a version of CP/M (I called ZCP/M as it was optimized for the Z-80). This was to be burned into a PROM and would sit in the 8-16k memory space (if I remember correctly). I got this to work (no small feat as the Timex system was a night mare to work with) but by this time the market was drying up and it never got released. I still have all of the code which is probably not of much use anymore. Those were incredibly fun times and it was a great group of people…

Clark Calkins

Chip Conway says:

Just heard Exatron the current company owned by Robert Howell is now up for sale. It will probably sell for $500K.

Ken Harlow says:

The good and the bad:

Good, the ESF was fast and neat. And you could buy Bill Gates' Level III Basic on a wafer, which was really great. This was Microsoft’s very first consumer product.

Bad, the “endless loop” system was prone to tangling and, over time, read failures. Like 8-track tapes, I suppose. But way better than casettes for sure.

Don’t remember anything ugly…

Zorba says:

I still remember reading about this, but never saw or owned one. But who can forget “System /12345”?

rjb says:

I have one of these, yes still have, packed away with my TRS-80. I loved it. It was fast and dependable, unlike the tape recorder storage. It turned my TRS-80 from a toy to a useful computer. I learned basic on that machine. Today some 35 years I’m a Visual Basic software developer.

Earles L. McCaul says:

Quoting from the PREFACE of my 1981 book, “TRS-80 Assembly Language Made Simple,":

“This book was written with the aid of a TRS-80 Model I computer equipped with Level II BASIC and 16K RAM, a Centronics 730 printer with Radio Shack Printer Interface Cable (26-1411), an Exatron ‘Stringy Floppy’ and Duncan Pittman’s ‘Type Right Secretary’ word-processing program.”

…so MANY years ago!

Albert Hartman says:

Zebra Systems sold the A&J Stringy Floppy for the ZX-81 and Timex/Sinclair 2068 in the 1980’s.

(I have 3" disks with the TS-2068 TOS and CP/M for the Timex Portugal Disk system [FDD-3000] which Zebra also sold.)