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1980s Computers Explanation of terms

The TRS-80 Model I

TRS-80 Model I


Tandy Radio Shack (US)


TRS-80 Model I

Date Launched

August 1977


£300 approx. without monitor

Microprocessor type

Zilog Z80A @ 1.77 MHz

ROM size

4 kilobytes (original Level I)
12 kilobytes (later Level II)

Standard RAM

4 kilobytes initially
16 kilobytes later

Maximum RAM

16 kilobytes internally
48 kilobytes with external expansion interface

Keyboard type

Typewriter style
Also available with a numeric keypad in place of the Radio Shack plate.

Supplied language

Tiny integer-only BASIC in Level I
Fully featured Microsoft BASIC in Level II

Text resolution

32 x 16 or 64 x 16 characters

Graphics resolution

128 x 48 pixels

Character graphics formatLike several other early machines, the TRS-80 had a character only display but could achieve the effect of high(ish) resolution graphics using a carefully designed character set:

Thus the first eight graphics characters were:
Character codes versus pixel patterns

Colours available


Example Screenshot

TRS-80 64-column screen
A promotional program by Tandy for the TRS-80. Note block graphics and absence of lowercase letters.
Lines of text appear widely spaced because each line was twelve pixels high but the actual font characters were only seven pixels.



Cassette load speed

250 baud

Dimensions (mm)
Weight (grams)

400 x 190 x 76
Not known

Special features

A matching monitor (actually an RCA television without a tuner) and disc drives were available.

Good points

Adequate specification for 1977.
Much cheaper than contemporary Apple and Commodore PET.
A considerable amount of software was available.

Bad points

Level I BASIC was very limited and only had three error messages (WHAT?, HOW? and SORRY).
Generated a large amount of radio and television interference. The Model I was unable to meet new FCC radio interference regulations and was eventually withdrawn and replaced by the Model III.
Reliability problems, especially in connecting to the expansion interface, earned it the nickname Trash-80.

How successful?

A very popular early computer, including in small businesses and schools in the US, selling over 250,000 and perhaps close to 1 million units.


The first of the low-cost home computers, the TRS-80 had a large following in the US and was quite popular in the UK.
Models II (1979), III and IV also appeared, being supplied with a monitor incorporating a floppy disc drive.

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