Picture of the day - July 17, 2005

A Vintage TRS-80 Computer

TRS-80 Computer System

Today's picture features the computer that truly made home computing available to the masses at an affordable price - the Radio Shack TRS-80 Model 1. Rudimentary by modern standards, the original TRS-80 sported a Zilog Z-80 CPU running at a clock speed of 1.77 Mhz.

There was no Disk Operating System such as Windows or Linux because there was no disk drive - programs and data were stored on cassette tapes. And as you can probably imagine, it took what seemed like an eternity to load a program from tape into the computer's memory so that it could be run (and every program had to be loaded every time you wanted to run it).

Since there was no operating system, the TRS-80 was operated and controlled directly from within a very limited version of the BASIC programming language that was stored on a 4 kilobyte Read Only Memory (ROM) chip. The "Level 1" version of BASIC that came standard in the original TRS-80 provided the user with the following error messages when something went wrong:
  • WHAT? - Indicated that a Syntax Error had occurred.
     
  • HOW? - Indicated that the running program had performed an illegal function, such as dividing by 0.
     
  • SORRY - The running program had used up all available memory.
As you can see, when an error occurred you were pretty much on your own while trying to find the cause of the problem.


The Random Access Memory (RAM) available in the original TRS-80 was either 4 kilobytes or 16 kilobytes, depending on whether you had an extra $300 or so to add to the purchase price. Yes, that's kilobytes, not megabytes!

And upgrading the RAM later was quite a hassle - there were no neat little memory modules that simply snapped into place way back then. Your TRS-80 came with 8 discrete RAM chips that had to actually be replaced, and the first models came with those chips soldered right onto the circuit board.

Later versions of the Model 1 had the RAM chips installed in sockets so they could be simply pulled out and replaced with higher capacity chips, but still, all but the bravest TRS-80 owners sent their computers back to Radio Shack and paid them to install the memory upgrade for them.

The monitor that came with the TRS-80 Model 1 was simply a 12 inch RCA black-and-white television set with the tuning circuitry left out and replaced by an RF Modulator. There was a place for a speaker to be mounted inside the monitor's case, but it was left empty - after all, there was no need for a speaker because the TRS-80 didn't have any sound capabilities whatsoever (quite ironic given the fact that programs and data were loaded from a cassette tape player).

The video display circuitry didn't support lower case characters - it was all upper case or nothing, even when doing word processing tasks! Third-party modifications were soon available however that enabled the use of lower case letters.

Other features were noticeably absent as well. For example, there was no "Real-Time Clock" circuitry so the computer didn't have a clue what time it was. There were also no serial ports, printer ports or any other types of ports for that matter except for the video and cassette tape player connections.

Radio Shack soon realized that they needed to add some expansion capabilities to the TRS-80, but since the CPU, RAM, ROM and the circuit board that held it all was contained inside the already cramped keyboard unit, they had to come up with another idea...

They settled upon an "Expansion Interface" box that was designed to sit underneath the monitor and connect to the keyboard unit with a flat 40 wire ribbon cable. The ribbon cable connections were constantly getting dirty which caused all kinds of errors and random computer restarts. This led to a temporary, but booming third party industry supplying gold-plated connectors that were soldered onto the original solder-covered connectors. Life with the TRS-80 was a little better after that.

The Expansion Interface box offered upgrade capabilities for the TRS-80 that included the following:
  • Total system RAM could be upgraded from a max of 16k to a max of 48k.
     
  • A Western Digital FD-1771 Floppy Disk Controller chip allowed up to 4 single-sided/single density floppy disk drives to be attached. Each floppy disk could store a whopping 160 kilobytes of programs and data!
     
  • A "Real-Time Clock" interrupt allowed the ROM BASIC powered CPU to keep track of the time.
     
  • A second cassette tape player interface allowed a dual cassette storage setup.
     
  • Printer and RS-232 serial ports were finally included.
The new and very popular capability to add up to 4 floppy disk drives meant that a Disk Operating System would be needed. This resulted in the hasty (and very buggy) production of TRS-DOS. The first widely distributed version of TRS-DOS was 2.1, a bug-riddled piece of software that would "lose" your programs and/or data at the most inopportune times.

TRS-DOS was never a very powerful or stable operating system, even in it's latest versions, but several third party software vendors came up with their own DOS's that operated very well with some features that were quite powerful for their times.

After reading all of this, you're probably thinking that I hated my old TRS-80 Model 1 with a passion, but nothing could be further from the truth. With the TRS-80, Radio Shack expanded the availability of computing power from the "white-coat" computer rooms of corporate America directly into the living rooms, basements and home offices of everyday people, and they did it at a remarkably low price for the time - $499 for the basic TRS-80 Model 1 with 4k of RAM.

That old technological dinosaur played a major role in getting an old country boy from the hills of southwestern Virginia interested in computers and all they had to offer to the modern world.

My beloved TRS-80 clearly showed me that technology would soon become the straightest path to our great nation's economic success...a path that would allow us to maintain and increase our lead as the world's number one economic and military superpower. It also helped convince me that there were more options for a country boy than just farming and factory work.
 

Picture Of The Day Homepage | Submit a photo

Interesting Articles