Tandy Computers

Tandy were one of the pioneers in the home computer market with the original TRS-80 Model 1, launched in 1978. Pictured above is a Model 4 computer, which was an evolution from the Model 1 but aimed more at the businesses or serious home users.

Here's further information on the Model 4 computer I owned (now sold):

Integrated 12" monochrome (green phosphor) display and high quality keyboard..
Two 5.25" floppy drives, sngle-sided, 184kB capacity.
Zilog Z80 8-bit processor running at 4MHz.
64kB RAM (sockets for additional 64kB), 14kB ROM for boot-strap and Microsoft Basic.
Centronics printer port, RS232 serial port and expansion bus edge connectors.

The Model 4 could run several different disc operating systems, TRSDOS, LDOS or NewDOS80, which offered similar capabilities (LDOS and NewDOS had more features). The display screen is 80 colums x 24 rows of text characters. The Model 4 could be put into Model III mode (by holding down the Break key then pressing Reset), which slowed the Z80 to 2MHz, and changed the display to 64 colums x 16 rows.

Please see Model 4 pictures, which also include a Tandy DMP-420 dot-matrix printer. Thanks go to Lorne Knowles in the USA for help with boot disks and printer cable.

The Model 4 has an Astec power supply (very similar to that in the Osborne 1, the Merlin Tonto and the Acorn BBC Master Compact), which had Rifa X capacitors which I replaced straight away, plus I replaced a bulging electrolytic capacitor. I also had to replace one of the floppy drives, these were clones of the Tandon TM100 labeled 'Texas Peripherals') with 80 tracks / single-sided. The machine was otherwise fine, and I sold it around 2015.

Pictures

This page was last revised on:8/5/21