TRS-80 Model I

The TRS-80 Model I was launched by Tandy Corporation (Radio Shack) in August 1977, just months after the Apple II and Commodore PET. It was one of the earliest ready-to-use personal computers, available pre-assembled and sold in Radio Shack stores across the U.S. It featured a Zilog Z80 processor, text-only monochrome display, and shipped with 4KB of RAM, expandable to 48KB. The TRS-80 came bundled with a monitor and cassette recorder, making it a truly turnkey solution. Its low price, widespread availability, and bundled TRS-DOS operating system helped it dominate the early U.S. computer market—especially among schools, businesses, and hobbyists.

Notable Features

• One of the “1977 Trinity” of early personal computers
• Sold as a complete system in thousands of Radio Shack stores
• Used Level I BASIC (from Tiny BASIC) and later Level II BASIC from Microsoft
• "Expansion Interface" added disk drives, serial ports, and printer support
• Became a huge hit in education, hobbyist, and early business sectors

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Historical Significance

• First personal computer to be mass-marketed via retail stores
• Quickly became the best-selling computer in the U.S. from 1977–1979
• Widely used in schools and small businesses across North America
• Created a huge third-party hardware and software ecosystem
• Spawned a long line of TRS-80 successors (Model III, IV, Color Computer, etc.)

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Collector's Notes

• Rarity: Moderate – many survive, but complete systems with expansion interface and disk drives are highly collectible
• Desirability: High – a vital piece of early computing history
• Common Issues:
  • Video interference and ghosting (due to bundled monitor and RF issues)
  • Keybounce or dead keys in keyboard units
  • Expansion Interface connectors prone to corrosion or instability
• Display Tips: Ideal setup includes original monitor, cassette recorder, and printed BASIC program running on-screen

Specifications

Technical Information
Name	TRS-80 Model I
Manufacturer	Tandy
Launched	Wednesday, August 3, 1977
Discontinued	1981-01-01
Launch Price	$599 (4K base model, monitor, and cassette recorder)
Country	United States
CPU	Zilog Z80 @ 1.77 MHz
Units Sold
Power	External PSU (power supplied through monitor and cabling)
Expansion	“Expansion Interface” provided extra RAM, RS-232, floppy support
Sound	None (some software used monitor relay for beeps!)
Storage	Cassette tape at 500 baud (optional Expansion Interface enabled floppy support)
Keyboard	Built-in full-size QWERTY keyboard (with numeric pad later added)
Graphics	None – no graphics modes (custom graphics via character blocks)
Display	64×16 text mode, monochrome CRT monitor (bundled)
ROM	4KB (includes BASIC interpreter)
RAM	4KB standard (expandable to 48KB)