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Apple II

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Apple II (original)
An early Apple II with floppy drives and monitor
Specifications
DeveloperApple Computer Company (Steve Wozniak)
ManufacturerApple Computer Company
TypeHome / personal computer[1]
ReleasedApril 1977 (West Coast Computer Faire)
DiscontinuedMay 1979 (replaced by Apple II Plus)[2]
Intro priceUS$1,298 (4 KB model)
US$2,638 (48 KB, two floppies, monitor)[3]
Units sold≈ 40,000 (original run)
CPUMOS Technology 6502 @ 1 MHz[4]
Memory4 KB RAM (standard)
Expandable to 48 KB on‑board†[5]
StorageBuilt‑in 1200‑baud cassette interface
Optional 5¼″ Disk II (140 KB) after 1978[6]
DisplayNTSC composite: 40 × 24 text
• Low‑res (40 × 48, 16 col)
• Hi‑res (280 × 192, 6 col)
Sound1‑bit piezo speaker (toggle via address $C030)[7]
Dimensions15.25 in W × 4.25 in H × 17.5 in D[8]
Weight≈ 11 lb (5 kg)[9]
OS / FirmwareBASIC in ROM • Apple DOS 3.1 / 3.2 (floppy) • ProDOS (1983+) [10]
PredecessorApple I
SuccessorApple II Plus
Model no.A2S001 (4 KB) • A2S002 (16 KB) • A2S003 (48 KB)[11]

The Apple II — often styled Apple ][ — was Apple’s first mass‑market microcomputer and the machine that ignited the late‑1970s home‑computer boom. Announced at the April 1977 West Coast Computer Faire, it combined color graphics, an integrated keyboard, BASIC in ROM, and eight open expansion slots in a single plastic enclosure — a radical departure from kit‑based contemporaries.

🕰️ Historical Context

  • Trinity of ’77: Launching alongside the Commodore PET 2001 and TRS‑80 Model I, the Apple II stood out for its color graphics and open slot bus.
  • From hobby to home: Ready‑to‑run BASIC and cassette I/O meant buyers could power up and program instantly, fostering a vast hobbyist software scene.
  • Disk II revolution (1978): Wozniak’s low‑chip‑count floppy controller cut drive cost in half, driving Apple II adoption in business and education.[12]

🛠️ Hardware Overview

Sub‑system Specification
CPU MOS 6502 @ 1.023 MHz (NTSC colour‑subcarrier ÷14)[13]
On‑board RAM 4 KB base (16 × 6116 SRAMs)
Sockets for 48 KB using eight 4 KB dynamic RAM banks†[14]
ROM 12 KB (Monitor + Integer BASIC + character generator)[15]
Graphics • Text 40 × 24, mixed text/lo‑res line
• Low‑res 40 × 48, 16 colors
• Hi‑res 280 × 192, 6 colors (+ artifact palette)[16]
Expansion Eight 50‑pin slot connectors (Slots 0‑7)
Disk II, serial, 80‑column, language card, etc.
I/O • Cassette in/out (mini‑jack) 1200 baud
• RF modulator or composite video out
• Game port (paddles/joystick)
• Speaker toggle ($C030)

† Later “language cards” piggy‑backed in Slot 0 to add 16 KB bank‑switch RAM, giving 64 KB total under DOS 3.3 or Apple Pascal.

Motherboard Revisions

  • Rev 0 & 1 (1977): 4‑layer PCB, raised power rails; sold through serial ≈ 15,000.
  • Rev 4 (1978): Cleaner DRAM timing, support for Integer/Applesoft BASIC ROM switch.
  • Rev 7 (1979): Last original‑run board — silkscreen “Apple Computer © 1978”.

💾 Software & Usage

  • Monitor prompt ( ] ) — power‑up to $FF69 Reset.
  • Integer BASIC in ROM; Applesoft BASIC supplied on cassette, later in ROM on II Plus.
  • Apple DOS 3.1 shipped with the Disk II (June 1978), automating LOAD/SAVE/BOOT.
  • Notable early titles: VisiCalc prototype, Adventureland, Lunar Lander, Apple Star‑Trek.

🔌 Expansion Ecosystem

Slot Typical Cards (1977‑79 era)
0 16 KB Language Card (Pascal) • CP/M Z‑80 (Microsoft SoftCard later)
1 80‑column video • Parallel printer
2 Serial interface • Modem 300 / 1200 baud
3 Parallel printer (Grappler) • Videx 80‑column
4 Game I/O • Speech Synthesizer
5 Disk II controller
6 Secondary Disk II (Slot 6 is boot slot by convention)
7 Memory expansion • Hard‑sector floppy • Ethernet (very late)

🧼 Maintenance & Restoration

Apple II motherboards are robust but susceptible to:

  • RAM socket corrosion — reseat or replace ICs.
  • RIFA line filters in early Astec PSUs — replace before they “magic smoke.”
  • Keyboard foam‑pad failure (Datanetics Type B) — modern foam disks restore feel.

Capacitor leakage is rare (all‑through‑hole design), but PSU electrolytics should be re‑formed or replaced after decades in storage.

Apple II Logic Board

📑 Documentation & Schematics

  • Apple II Reference Manual (blue cover, 1977) — full schematics, Woz Monitor listings.
  • Apple DOS Manual (1978) — Disk II architecture, DOS 3.1 commands.
  • Apple II Schematics — Apple II Schematics

Scanned PDFs are archived on the Apple Documentation page.

🧑‍🔧 Technical Details

System Architecture at a Glance

Sub-system Apple II Specification (Rev-0 / Rev-01, Apr 1977 – ’78)
CPU MOS 6502 @ 1.023 MHz (NTSC color-burst ÷ 14)
Address bus / Data bus 16-bit addr. • 8-bit data ⇒ 64 KB logical space
ROM 12 KB total
  • 2 KB WOZ Monitor (F800–FFFF)
  • 10 KB Apple Integer BASIC (E000–F3FF)

Rev-0 shipped with 10 KB; later Rev-01 raised to 12 KB

RAM (base) 4 KB DRAM (18 × 4116, 200 ns) — optional 4 KB/16 KB kits
RAM (max, mainboard) 48 KB (three 16 KB banks, address-select jumpers)
Expansion RAM +16 KB "Language Card" (slot 0, 1980) ⇒ 64 KB total
Video • Text 40 × 24 (upper-case, inverse)

• Lo-Res 40 × 48 (16 colors) • Hi-Res 280 × 192, 6 colors + NTSC artifact hues Shift-register DMA steals cycles every micro-line

Sound One-bit speaker toggled by writing any address in $C030 range (~1 µs click)

Software PWM enables simple music

Mass Storage 1200-baud cassette interface (port C060/61)

Disk II controller (1978+) 143 KB 5.25″ GCR

I/O, fixed Game I/O (paddle/joystick) • Cassette IN/OUT • Composite video • RF modulator header
Expansion Eight 50-pin slots (0–7) full CPU bus, IRQ, DMA; 3 MHz max load

Slot 6 pre-wired for Disk II; slot 0 firmware (autostart)

Default Memory Map (No Language Card)

Apple II 48 KB Map
Range (hex) Size Use
$0000 – $BFFF 48 KB User RAM (three 16 KB banks)
$C000 – $C07F 128 B Peripheral soft-switches (keyboard, speaker, paddles)
$C080 – $C0FF 128 B Peripheral slot I/O (reads/writes to slot 0–7 cards)
$C100 – $C7FF 1.5 KB Slot ROMs (256 B each × 6)
$C800 – $CFFF 2 KB Firmware bank (usually Disk II)
$D000 – $FFFF 12 KB Integer BASIC & Monitor ROM
  • Soft-switches* at $C050–$C057 flip graphics/text, hires/lores, full/half screen, etc.

Video Timing & Color Generation

Parameter Value (NTSC)

/ hi-res /

Pixel clock 14.31818 MHz / 1 = 14.318 MHz (color sub-carrier × 4)
Horizontal total 455 px (280 active)
Vertical total 262.5 lines (192 active)
Refresh rate 59.94 Hz
Color method 1-bit pairs create 3.58 MHz phase shifts → *artifact* green, purple, orange, blue

Expansion Slots — Electrical Pin-out (abridged)

Pin Signal Description Pin Signal Description
1 –12 V –12 V @ 100 mA 26 A4 CPU address 4
2 +12 V +12 V @ 400 mA 27 A3 Address 3
3 NMI Non-Mask Int. in 28 A2 Address 2
4 IRQ IRQ in 29 A1 Address 1
5 RDY DMA ready out 30 A0 Address 0
6 PHI0 6502 Ø0 out 31 D0 Data 0
… … … … … …
50 GND Ground return

Slots source full 1 MHz Φ2 and 14 MHz dot clock for video cards.

Apple Disk II

Disk II (1978) Quick Specs

  • Controller: 8-bit state-machine in 256-byte PROM (Steve Wozniak)
  • Encoding: Group-Code Recording, 13 sector × 35 tracks → 143,360 bytes
  • Transfer rate: ~15 kB s⁻¹; CPU bit-banged (no DMA)

Performance Benchmarks (BYTE Jan 1978)

Test Apple II 4 KB TRS-80 I (4 KB) Comment
BASIC loop (1000 FOR…NEXT) 18.8 s 24.7 s Integer BASIC faster than TRS Level I
16-color Lo-Res fill 0.21 s — Unique color graphics edge
Cassette load 2 KB 25 s 49 s “Kansas City” 1200 baud beats 500 baud

Revision History

Rev Board Marker Key Changes
Rev-0 820-0001-00 No silkscreen, paddle trim pots, noisy video; shipped Apr-Aug 1977 (≈6,000 units)
Rev-01 820-0001-04 Improved video timing, added color – burst delay line; fall ’77
Rev-02 820-0001-07 Sockets for 16 KB DRAM, CPU ceramic → plastic; early ’78
Rev-03 820-0001-10 Pre-wired for Language Card, stronger +5 V regulator; late ’78

Notable Engineering Traits & Trivia

  • Floating-bus video DMA: display circuitry steals DRAM access on every Φ2 low, imposing deterministic “video glitch” timing exploited by games.
  • Annunciator outputs (addresses $C04E–$C05B) allow slot cards to flip soft-switches or drive relay boards.
  • Speaker click length equals one CPU instruction — programmers play music by carefully timed loops.
  • The iconic “BEEP!” is a 65-cycle loop toggling $C030 at 256 µs intervals.
  • First home computer with full color graphics on a cheap TV via NTSC artifacting.

🧰 Replica & Emulation Resources

  • Replica II — Gerber‑faithful four‑layer re‑creation using modern DRAM.
  • AppleWin / LinApple / MAME — full‑speed software emulators supporting Integer & Applesoft ROM sets and DOS/ProDOS disk images.

🌟 Legacy

The expandable slot architecture, affordable Disk II, and the industry‑shifting spreadsheet VisiCalc made the Apple II the first commercially successful mass‑produced microcomputer, cementing Apple’s future and inspiring clones worldwide (Franklin Ace, Basis 108, ITT 2020).

  1. ↑ Apple II—link(accessed 2024-06-20)
  2. ↑ Apple II History: The Apple II Plus—link(accessed 2024-06-20)
  3. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  4. ↑ Apple II—link(accessed 2024-06-20)
  5. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  6. ↑ Apple II History: The Disk II—link(accessed 2024-06-20)
  7. ↑ Apple II History: Sound—link(accessed 2024-06-20)
  8. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  9. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  10. ↑ Apple II History: Operating Systems—link(accessed 2024-06-20)
  11. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  12. ↑ Apple II History: The Disk II—link(accessed 2024-06-20)
  13. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  14. ↑ Apple II (original) - Old Computers—link(accessed 2024-06-20)
  15. ↑ Apple II—link(accessed 2024-06-20)
  16. ↑ Apple II—link(accessed 2024-06-20)
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