Macintosh Classic
 | |
| 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 |
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.
General Maintenance
[edit | edit source]For cleaning, battery maintenance, board inspection, and power supply tuning, refer to the Macintosh Classic General Maintenance page.
PCB Schematics & Service Manual
[edit | edit source]The 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 | edit source]
All Apple Service Manuals can be found on the Apple Service Source page.
Logic Board & Analog Board Schematics
[edit | edit source]| Logic Board | Analog Board |
|---|---|
 |
 |
Capacitor Replacement Guide
[edit | edit source]Full details on logic and analog board recapping can be found at the Macintosh Classic Capacitor Replacement Guide.
Retrobrite
[edit | edit source]To restore the beige color of the Classic’s case, refer to the safe plastic whitening procedures outlined on the Retrobrite page.
Troubleshooting
[edit | edit source]For 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
[edit | edit source]System Architecture at a Glance
[edit | edit source]| 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 | edit source]| 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 | edit source]| 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 | edit source]- 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 | edit source]- 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 | edit source]- 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
[edit | edit source]68000 → 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 | edit source]| 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 | edit source]| 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 | edit source]- 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.