Macintosh 512K
 | |
| Specifications | |
|---|---|
| Manufacturer | Apple Computer, Inc. |
| Type | Personal computer |
| Released | September 10, 1984 |
| Discontinued | April 14, 1986 |
| Intro price | US$3,195 |
| CPU | Motorola 68000 @ 7.83 MHz |
| Memory | 512 KB RAM (not expandable) |
| Storage | 400 KB 3.5″ floppy drive |
| Display | 9″ monochrome CRT (512 × 342 px) |
| Sound | Monaural 8‑bit, 22 kHz (4‑voice) |
| Dimensions | 13.6″ H × 9.6″ W × 10.9″ D |
| Weight | 16.5 lb (7.5 kg) |
| OS / Firmware | System 1.0 – System 4.1 |
| Predecessor | Macintosh 128K |
| Successor | Macintosh 512Ke |
| Codename | Engine, Hero |
| Model no. | M0001W |
The Macintosh 512K, released on September 10, 1984, was an improved version of the Macintosh 128K. It featured four times the RAM (512 KB), allowing for improved multitasking and compatibility with a wider range of software. It retained the same Motorola 68000 processor running at 7.83 MHz and the 9-inch monochrome display with a 400 KB floppy disk drive.
Due to its increased memory, the Macintosh 512K could run more advanced applications, including MacDraw, MacProject, and Microsoft Multiplan. However, it still lacked built-in support for an internal hard drive, relying on external floppy drives for additional storage. The 512K model was succeeded by the Macintosh Plus, which introduced expandable RAM and an external SCSI port.
Maintenance
[edit | edit source]Due to the 512K's similarities with the 128K, there is no difference in it's maintenance, PCB or Schmatics, please see the Macintosh 128K page for maintenance, guides and more information.
Technical Details
[edit | edit source]System Architecture at a Glance
[edit | edit source]| Sub-system | Specification |
|---|---|
| CPU | Motorola 68000 @ 7.8336 MHz (15.667 MHz ÷ 2) |
| Bus width | 16-bit data • 24-bit address (16 MB logical space) |
| ROM | 64 KB “Boot/Toolbox” (4 × 16 KB HN462716 mask ROMs) |
| RAM | 512 KB DRAM (16 × 256-Kbit 150 ns) – *soldered, non-expandable* |
| Video | 512 × 342 monochrome frame-buffer (22.1 KB) DMA-shared with system RAM |
| Sound | 8-bit PWM DAC via VIA timers • 22 kHz low-pass to speaker / 3.5 mm jack |
| Disk I/O | Sony OA-D34V 400 KB GCR 3.5″ drive • IWM controller |
| Ports | DE-9 mouse/KB • DB-19 ext. floppy • RS-422 serial × 2 (230 kbps) • 3/8″ audio-out |
Memory Map (Physical)
[edit | edit source]| Range | Size | Purpose |
|---|---|---|
| $000000 – $07FFFF | 512 KB | DRAM (program, frame-buffer, stack, heap) |
| $400000 – $41FFFF | 128 KB | ROM (Boot + Toolbox) |
| $480000 – $4BFFFF | 256 KB | I/O space (VIA 1 & 2, SCC, IWM, VBL PAL) |
| $500000 – $5FFFFF | 1 MB | Reserved / not decoded |
| $600000 – $FFFFFF | Mirrors / “ghost ranges” |
- Frame-buffer note:* display memory occupies $07B000 – $07FFFF (22,016 bytes).
DMA steals cycles from the 68000 only during active scan-lines, identical to the 128 K.
ROM Layout (64 KB)
[edit | edit source]| Offset | Size | Module (v3.3 ROM set) |
|---|---|---|
| $400000 | 8 KB | 68000 vectors + mini-shell |
| $402000 | 16 KB | QuickDraw 1.0 (mono) |
| $406000 | 20 KB | Macintosh Toolbox routines |
| $40B000 | 12 KB | SANE (IEEE fp) + traps |
| $40E000 | 8 KB | Sony IWM floppy driver / boot |
Video Timing
[edit | edit source]| Parameter | Value (NTSC) |
|---|---|
| Pixel clock | 7.833 MHz |
| Horizontal total | 704 px (512 active) |
| Vertical total | 370 lines (342 active) |
| Refresh rate | 60.15 Hz |
Floppy-Disk Format
[edit | edit source]- 80 tracks • single-sided variable-speed GCR
- 12 sectors/track (outer) → 8 sectors/track (inner)
- 512-byte sectors • 400 KB formatted capacity
Key I/O ICs
[edit | edit source]- 6522 VIA × 2 – system timers, sound PWM, keyboard/mouse handshake
- 8530 SCC – dual RS-422 serial ports
- IWM – “Integrated Woz Machine” floppy controller
- MC6883 PAL – VBL interrupt generator & DRAM time-slot arbiter
Sound Path
[edit | edit source]The 68000 writes 8-bit samples to VIA Port A. VIA Timer 1 toggles Port B at 22.254 kHz, producing pulse-width-modulated audio → RC filter → LM380 amplifier → speaker/headphone jack.
Hardware Easter Egg
[edit | edit source]- Hold* ⌘ + ⌥ + ⇧ + Clear at boot to hear the hidden “bass” startup chime.
(The 512K retains this ROM routine; it was removed in the 512Ke/Plus.)