TRS-80 Model 1

Launched by Tandy Corporation on August 3, 1977, the TRS-80 Model I was one of the original "1977 Trinity" home computers, alongside the Apple II and Commodore PET. Sold through Radio Shack stores across the U.S., it featured a Zilog Z80 CPU, monochrome display, and 4KB of RAM, all in an affordable, ready-to-use package. With its bundled monitor and cassette recorder, it introduced thousands of users to computing. Despite hardware limitations and early bugs, its price and accessibility helped it dominate the U.S. market in the late 1970s.

Notable Features

• Included monitor and cassette in the base bundle – turnkey operation
• Level I BASIC in ROM; Level II added variables, string handling, and better speed
• “Expansion Interface” added RAM, RS-232, floppy support, and printer port
• Quickly adopted in education, hobby computing, and small business applications
• Massive third-party software and hardware ecosystem developed by 1980

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Historical Significance

• One of the first pre-assembled personal computers widely available at retail
• Helped popularize the Z80 CPU and BASIC programming
• Dominated U.S. computer sales in 1978–79
• Common platform for early business software, games, and homebrew applications
• Paved the way for later TRS-80 models including Model III, 4, and Color Computer

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Collector's Notes

• Rarity: Moderate – common in North America, but harder to find complete bundles
• Desirability: High among early microcomputer collectors and Z80/BASIC enthusiasts
• Common Issues:
  • Video interference (“snow”) due to poor shielding
  • Cassette drive misalignment or dropout
  • Expansion Interface reliability and connection instability
• Display Tips: Showcase with bundled monitor, cassette recorder, and Star Trek or Lunar Lander BASIC programs running on-screen

Specifications

Technical Information
Name	TRS-80 Model 1
Manufacturer	Tandy
Launched	Wednesday, August 3, 1977
Discontinued	January 1981 (replaced by Model III)
Launch Price	$599 USD (with monitor and cassette deck)
Country	United States
CPU	Zilog Z80 @ 1.77 MHz
Units Sold	~250,000
Power	External PSU (power passed through monitor to keyboard unit)
Expansion	Expansion Interface added floppy support, RS-232, printer ports
Storage	Cassette recorder (500 baud) or floppy via optional Expansion Interface
Keyboard	Full-travel 53-key keyboard (alphanumeric, no lowercase initially)
Sound	None (software used monitor relay for crude sound effects)
Graphics	No bitmap graphics (simulated via semigraphics in text mode)
Display	64×16 character monochrome text (black & white monitor included)
ROM	4KB Level I BASIC (8KB Level II BASIC with upgrade)
RAM	4KB standard (expandable to 48KB with Expansion Interface)