The Model III is basically an upgrade of the TRS-80 Model I. It was released in July 1980, three years after the Model I. It has the same Z-80 CPU, but it is faster (2.03 MHz), has more memory, and the floppy drives hold twice as much data, although the Model I could be upgraded to some of these features. The Model III was advertised as being backwards compatible with the majority of software created for the Model I. The Model III had two cassette data rate options - low speed, 500 baud, which accepted tapes recorded on a Model I, and a new higher speed, 1500 baud.

The major reason for developing the Model III was because the FCC had just instituted new regulations about RF emissions generated by computers and other electronic devices. The Model I was completely unshielded and was unable to pass the emission restrictions.

The Model III system is entirely self-contained and includes a 53-key keyboard with 12-key numeric pad, 12-inch video monitor, and space for twin 5.25-inch disk drives. The original Model I had edge-type connectors with ribbon cable connecting the keyboard to the (optional) Expansion Interface, as well as the floppy drives. This type of connection was very unreliable, and led to the occasional system crash or lock-up.

The were five versions of the Model III available:

• Level I Basic with 4K RAM (26-1061)
• Model III (Level II) Basic with 16K RAM (26-1062)
• Model III (Level II) Basic with 32K RAM and double disk drive (26-1063)
• Model III (Level II) Basic with 48K RAM and single disk drive (26-1065)
• Model III (Level II) Basic with 48K RAM and double disk drive (26-1066)

This example in our collection is the 26-1066 version.

Manufacturer: Radio Shack
Date: July 1980

This exhibit has a reference ID of CH51417. Please quote this reference ID in any communication with the Centre for Computing History.

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