Macintosh Classic
The Macintosh Classic was introduced by Apple on October 15, 1990, as a low-cost alternative in the Macintosh lineup and a spiritual successor to the original Macintosh 128K and SE/30. It retained the same 9-inch monochrome display and compact form factor, but included a 1.44 MB SuperDrive and optional internal SCSI hard drive. It was the first Macintosh to sell for under $1,000, making it a popular choice for schools and home users.
 | |
| Macintosh Classic | |
| Specifications | |
|---|---|
| Manufacturer | Apple Computer, Inc. |
| Type | Personal Computer |
| Released | October 15, 1990 |
| Discontinued | September 14, 1992 |
| Intro price | US$999 – $1,499 |
| CPU | Motorola 68000 @ 8 MHz |
| Memory | 1 MB RAM (expandable to 4 MB) |
| Storage | 1.44 MB 3.5" floppy drive, optional 40 MB SCSI hard drive |
| Display | 9" monochrome CRT (512×342 pixels) |
| Sound | Monaural 8-bit, 22 kHz |
| Dimensions | 13.2" H × 9.6" W × 10.9" D |
| Weight | 16.5 lbs (7.5 kg) |
| OS / Firmware | System 6.0.7 – System 7.5.5 |
| Predecessor | Macintosh SE/30 |
| Successor | Macintosh Classic II |
| Codename | Elsie, Skywriter |
| Model no. | M0420 |
General Maintenance
editFor cleaning, battery maintenance, board inspection, and power supply tuning, refer to the Macintosh Classic General Maintenance page.
PCB Schematics & Service Manual
editThe Macintosh Classic includes two main PCBs: a unified logic board and an analog board. Below are the schematics and Apple’s official service manual.
Apple Service Manual
edit
All Apple Service Manuals can be found on the Apple Service Source page.
Logic Board & Analog Board Schematics
edit| Logic Board | Analog Board |
|---|---|
 |
 |
Capacitor Replacement Guide
editFull details on logic and analog board recapping can be found at the Macintosh Classic Capacitor Replacement Guide.
Retrobrite
editTo restore the beige color of the Classic’s case, refer to the safe plastic whitening procedures outlined on the Retrobrite page.
Troubleshooting
editFor diagnosis and solutions to common issues including no startup, checkerboard patterns, floppy drive problems, and failed PRAM batteries, see the Macintosh Classic Troubleshooting guide.
Technical Details
editSystem Architecture at a Glance
edit| Sub-system | Specification (Macintosh Classic, Oct 1990) |
|---|---|
| CPU | Motorola 68000 @ 7.8336 MHz (15.667 MHz ÷ 2) |
| FPU | — (none; not socketed) |
| Bus width | 16-bit data • 24-bit address (16 MB logical) |
| ROM | 512 KB “SE/30-class” ROM SIMM (v7.0) — 32-bit clean, HFS+, Color QD |
| RAM | 1 MB soldered • Expansion card adds 1 MB + 2 × 30-pin SIMM slots → 4 MB max |
| Video | 512 × 342 monochrome — 22.1 KB DMA steal from main DRAM |
| Sound | 8-bit PWM DAC via VIA timers • 22 kHz → RC filter → LM380 amp |
| Disks | Internal Sony SWIM-II 800 KB (FDHD option 1.44 MB) • 40 MB SCSI HDD (BTO) |
| Ports | ADB • DB-19 ext. floppy • DB-25 SCSI-1 • Geo/SCC serial × 2 • 3.5 mm audio-out |
| Expansion | No PDS; memory–I/O expansion via proprietary 96-pin mezzanine card |
Memory Map (Physical)
edit| Range | Size | Purpose |
|---|---|---|
| $0000 00 – $0FFF FF | 1 MB | On-board DRAM |
| $1000 00 – $4FFF FF | 4 MB | Expansion DRAM (if present → 4 MB ceiling) |
| $4000 00 – $47FF FF | 512 KB | ROM SIMM (v7.0) |
| $5000 00 – $50FF FF | 64 KB | I/O bank A – VIA 1/2, SCC, SWIM-II, ADB, VBL PAL |
| $5800 00 – $58FF FF | 64 KB | SCSI NCR 53C80 regs + glue |
| $5C00 00 – $5FFF FF | 256 KB | Expansion card decode (memory & option EEPROM) |
| $9000 00 – $9000 FF | 256 B | Frame-buffer shift register (mirrored) |
| $C000 00 – $FF FF FF | Mirrors / reserved |
ROM SIMM Layout (512 KB, v7.0)
edit| Offset | Size | Module |
|---|---|---|
| $4000 00 | 16 KB | 68000 vectors & Mini-Shell |
| $4004 00 | 64 KB | QuickDraw 1.3 (monochrome & color, 32-bit) |
| $4014 00 | 192 KB | Toolbox, Window/Menu mgrs., SANE FP |
| $4044 00 | 80 KB | SWIM-II floppy, ASC sound, ADB Egret |
| $405E 00 | 96 KB | SCSI Manager 4.3, Disk Cache, HFS/HFS+ |
SWIM-II Floppy Controller
edit- 800 KB GCR variable-speed (standard)
- FDHD build-to-order: 1.44 MB MFM + 800 KB GCR (autodetect)
- Supports intelligent-step motor timing; faster reads on outer tracks.
SCSI & Mass-Storage
edit- NCR 53C80 8-bit controller — 5 MB s⁻¹ sync (≈1.1 MB s⁻¹ async real-world)
- “Pseudo-DMA” using block-moves by CPU; internal drive on 50-pin ribbon.
Key I/O ICs
edit- 6522 VIA × 2 — system timers, sound PWM, keyboard‐handshake
- 8530 SCC — dual RS-422 serial (up to 230 kbps)
- SWIM-II — floppy & GCR/MFM selector
- NCR 53C80 — SCSI
- Egret (68HC05) — ADB, soft-power, PRAM battery
Sound Path
edit68000 → VIA Port A (8-bit sample) • VIA Timer 1 @ 22.254 kHz toggles Port B → PWM → RC filter → LM380 → speaker / rear jack.
RAM Expansion Notes
edit| Total RAM | Expansion Card SIMMs | Jumper |
|---|---|---|
| 2 MB | none (card only) | “No SIMMs” (JP top) |
| 2.5 MB | 2 × 256 KB | “With SIMMs” (JP bottom) |
| 4 MB | 2 × 1 MB | “With SIMMs” (JP bottom) |
- SIMMs: 30-pin, 120 ns, 8-chip, non-parity only.
- Mixed sizes not supported; SIMMs must match pair.
Performance Benchmarks
edit| Test (MacBench 1.0) | Score | vs Mac Plus |
|---|---|---|
| CPU integer | 115 | × 1.43 |
| Disk (40 MB SCSI) | 230 | × 1.92 |
| Graphics (QD) | 100 | × 1.00 |
| Overall | 123 | × 1.53 |
Hardware Trivia
edit- Last 68000-based Macintosh; ROM identical to SE/30 but 32-bit addressing disabled.
- “*Seattle*” logic board codename; early EVT boards silk-screened “LittleFish”.
- Easter egg: type `G 40E053` in MacsBug to reveal the original compact-Mac developers list.