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TRS-80 Model I

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Early Intel and Zilog CPU

based portable personal



TRS-80 Model I

TRS-80 Model III

TRS-80 Model IV

Color Computer

Color Computer 2

Color Computer 3



Early ultra-light personal

computers based on Intel

and Zilog CPU's.  These

units are all unique in

their class.

TRS-80 Model II

Tandy Model 12

Tandy Model 16, 16b



Once again systems

caught between CPU


TRS-80, Tandy 2000

Tandy 1200

MC 10



Simply the best personal

computers built. 

Operated under MS-DOS

2.11 to 6.22.  Based on

the IBM PC. Jr.

Tandy 1000, 1000a

Tandy 1000SX ,1000TX

Tandy 1000 SL,TL & TL2

Tandy 1000EX, 1000 HX

Tandy 1000 RL, RLX

Released: August 1977
CPU: Zilog Z-80A, 1.77 MHz
RAM: 4K, 48K max
Ports: Cassette I/O, Expansion connector
Display: 12" monochrome monitor, 64 X 16 text
Expansion: External Expansion Interface
Storage: Cassette storage, External 87K floppy drive
Operating System: BASIC in ROM

Although Tandy held for some time that the

Model I was the first personal computer sold, the

Apple unfortunately holds that distinction.  What is

noteworthy is that the TRS-80 Model I was the first

personal computer that was mass marketed in

North America and then to the UK.  This was accomplished through Radio Shack, a

division of Tandy Corporation.


The Model 1 came with 4K RAM standard and a  Basic called "Basic Level 1".  The

monitor was essentially an RCA TV with the tuner removed. File storage was on cassette

tape. The Model 1 could be upgraded to 16Kb and Level 2 Basic. Expandability was

gained through the Expansion Interface. This was a base unit connected to the back of the

Model 1 with a short  ribbon cable. The composite TV monitor then sat on top of the

Expansion Interface. With an Expansion Interface, you could add additional memory,

control serial devices, use two tape decks instead of just one, and control up to four floppy



Many found the Model I troublesome with the expansion unit.  Edge card connections in

many climates would corrode, and lose connection causing the unit to fail.  Regular

maintenance could prevent further difficulties.  The Model I also had edge card

connections for 5.25" floppy drives, single sides, which could be chained up to 4 drives. 

The operating systems  (DOS) were many including TRS-DOS, and NewDos 80. 


Many Model I survive today and can be seen on eBay for auction daily, and are collectors

items fetching good dollars.  If your lucky to have one of these you will not have any

trouble finding someone to take it off your hands.  The writer included.  :-)



(c) 2004, 2005 Brian K. Hahn

 All Rights Reserved.