TRS-80 Model I

26-1002 · 1977–1981 · desktop

Specifications

Cpu: Zilog Z80, 1.77 MHz
Ram: max: 48 KB with a Tandy Expansion Interface · base: 4 KB
Ports: Cassette in/out · Expansion Interface bus connector · Built-in monitor (integrated, not a separate port)
Display: Built-in monochrome monitor, 64×16 text (32×16 in wide mode), block graphics
Storage: base: Cassette tape via a standard cassette recorder (no internal storage) · options: 5.25" floppy disk drive(s) via the Expansion Interface
Os Support: latest: TRSDOS with Level II (Microsoft) BASIC · shipped: Level I BASIC in ROM
Release Price: $599.95 (with monitor and cassette recorder)

Variants

Revisions

Level I BASICLevel I1977 launch ROM, paired with 4K RAM

Level II BASICLevel II1978 onward, required 16K RAM minimum

Storage

4KB RAMoriginal 1977 cassette configuration

16KB RAMcommon configuration with Level II BASIC

Upgrade paths

RAM

48 KB via the Tandy Expansion Interface · The Expansion Interface is a separate box that sits under the keyboard unit, adding RAM up to 48 KB, a floppy controller, and a real parallel printer port.

MODERATE

storage

Up to 4 external 5.25" floppy drives via the Expansion Interface's disk controller · Turned a cassette-only machine into a disk-based system, the configuration most Model I software libraries assumed.

MODERATE