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TRS-80 Model 4

26-1067 · 26-1068 · 26-1069 · 1983–1985 · desktop

Specifications

Cpu: Zilog Z80A, 4 MHz
Ram: max: 128 KB via community RAM chip swap (16-pin 4164 DRAMs plus, on early non-gate-array boards, an added PAL chip) · base: 64 KB
Ports: Cassette in/out · RS-232 serial (optional board) · Parallel printer port · Expansion interface bus
Display: Built-in 12" monitor, 80x24 text (also selectable 64x16 for Model III compatibility)
Storage: base: One or two internal 5.25" single-sided floppy drives (180 KB each), depending on configuration · options: No internal drive (diskless configuration with cassette only) · RS-232 serial board and port
Os Support: latest: CP/M Plus (community and third-party support), plus TRSDOS 6 · shipped: TRSDOS 6 / Model III BASIC in ROM, backward-compatible with Model III software
Release Price: $999 (diskless, 16 KB configuration); $1,699 (64 KB, single drive)

Variants

Revisions

Model 4 (diskless)16 KB RAM, no floppy drive, cassette-only, 1983

Model 4 (single drive)64 KB RAM, one floppy drive, 1983

Model 4 (dual drive with RS-232)64 KB RAM, two floppy drives, serial port, 1983

Model 4D1985 revision, double-sided drives and a socketed gate array replacing several discrete chips

Upgrade paths

RAM

128 KB via an 8-chip 4164 DRAM swap (plus a PAL/gate-array fix on early boards) · Well documented in the vintage-computing community (VCF forums), but early non-gate-array Model 4 boards need an extra PAL chip to address the additional memory correctly, a step that trips up a lot of first attempts.

~$20-40 for chips

HARD

storage

Second internal 5.25" floppy drive, or external drives via the expansion interface · Single-drive units have an empty bay for the second drive.

~$150-300 at the time

MODERATE

ports

RS-232 serial board, add-on card

~$100 at the time

EASY