Commodore 64

Overview

The Commodore 64 (C64) arrived in January 1982 with 64KB of RAM, arcade-quality graphics and sound chips, and a $595 price tag that undercut every competitor. It became the best-selling single computer model in history (12-17 million units), anchoring bedroom coding culture, game development, and the demoscene for over a decade.

Technical Specifications

Processor

MOS Technology 6510 @ 1.023 MHz (NTSC) / 0.985 MHz (PAL)

8-bit CPU based on 6502
56 instructions, 13 addressing modes
Built-in 6-bit I/O port for memory banking
~400,000 instructions per second

Memory

64KB RAM organized as:

$0000-$9FFF: 40KB program RAM
$A000-$BFFF: 8KB BASIC ROM (can be banked out)
$C000-$CFFF: 4KB RAM (under I/O)
$D000-$DFFF: 4KB I/O + colour RAM
$E000-$FFFF: 8KB KERNAL ROM (can be banked out)

1KB colour RAM at $D800-$DBFF (independent of main memory)

Graphics: VIC-II Chip

MOS 6567 (NTSC) / 6569 (PAL)

320×200 hi-res bitmap or 40×25 text modes
160×200 multicolour mode (4 colours per 4×8 cell)
8 hardware sprites (24×21 pixels each)
16-colour palette
Smooth scrolling, collision detection, raster interrupts
Steals CPU cycles on “badlines” for screen refresh

Sound: SID Chip

MOS 6581 (early) / 8580 (later)

3 independent oscillators
4 waveforms: triangle, sawtooth, pulse, noise
ADSR envelope per voice
Multimode filter (low-pass, high-pass, band-pass)
Ring modulation and oscillator sync
8-bit volume control

I/O Ports

2× CIA chips (6526): Keyboard, joystick, timers, serial port
Cassette port: Datasette tape drive
Serial port: 1541 disk drive (proprietary fast serial)
User port: RS-232, modems, hardware expansions
Cartridge port: 16KB ROM cartridges, freezers, RAM expansion

Storage

Datasette: Cassette tapes, 300 baud (~1500 bytes/sec)
1541: 5.25” floppy disk, 170KB capacity, notoriously slow
Cartridges: Instant-load games, freezers, utilities

Programming Environment

BASIC V2

Built-in interpreter (Commodore BASIC 2.0)

Based on Microsoft 6502 BASIC
Limited compared to competitors (no sound/graphics commands)
Extended via POKE for hardware access
Line numbers 0-63999
38KB available for programs (after BASIC ROM)

Common workflow:

Type program in BASIC
POKE hardware directly for graphics/sound
Embed machine code for speed (SYS command)

Machine Language

Direct 6510 assembly for maximum performance

Games and demos almost exclusively machine code
Assemblers: VICMON, DASM, ACME, KickAssembler
~10-50× faster than BASIC
Required for raster effects, sprite multiplexing, music

Memory Banking

The 6510’s I/O port ($0001) banks ROM/RAM:

Bank out BASIC ROM for 8KB extra RAM
Bank out KERNAL for another 8KB
Bank out I/O/charset for full 64KB RAM
Critical for games needing maximum memory

Why It Mattered

Affordability

Commodore owned MOS Technology (chip fab), letting them price aggressively. The C64 launched at $595 when competitors charged $1000+. By 1983, it sold for $200. By 1990, under $100. Every kid could afford one.

Creativity Platform

Bundled BASIC invited experimentation. Type-in listings from magazines (Compute!, ZZAP!64, RUN) taught programming. POKE commands unlocked hardware features. No barriers—turn it on, start coding.

Ecosystem

Software: 10,000+ commercial games, vast public domain library
Hardware: Cartridges, modems, RAM expansions, MIDI interfaces
Scenes: Demoscene, music (SID), cracking groups, BBSes
Longevity: Production ran 1982-1994, active use into 2000s

Cultural Impact

The C64 created a generation of programmers. Bedroom coders became industry professionals. Demo coders pioneered techniques (copper bars, FLI, sprite multiplexing) that influenced later platforms. The machine taught: hardware is yours to control.

Quirks and Limitations

The 1541 Disk Drive

Notoriously slow—takes 1-2 minutes to load a game due to serial bus design. Games used custom fastloaders (reducing load to 15-30 seconds) or multi-load schemes. Tape was faster for small programs but lacked random access.

BASIC V2 Limitations

No commands for sprites, sound, or graphics—everything via POKE. Other 8-bits (BBC Micro, Atari) had graphics BASIC commands. C64 programmers learned hardware registers from day one.

Colour Limitations

16 colours total, but text mode limits you to 2 colours per 8×8 cell (foreground + background). Multicolour mode gives 4 colours but halves horizontal resolution. Sprites help—add moving colour independently.

Badlines

VIC-II “steals” CPU cycles every 8th raster line to refresh screen data. Code that’s fast 7/8 of the time suddenly slows down. Games learned to time around badlines or disable the screen during critical operations.

Modern Legacy

Emulation

VICE: Cycle-accurate emulation for all platforms
CCS64: Windows emulator with great compatibility
MiSTer FPGA: Hardware-level recreation
Online emulators in browser (JavaScript C64)

Hardware Revivals

THE C64 Maxi/Mini: Official replicas with built-in games
Ultimate 64: FPGA motherboard replacement
1541 Ultimate II+: SD card floppy emulation
MEGA65: Modern 8-bit with C64 compatibility

Active Community

New games released annually: Commercial and homebrew
Demo parties: Revision, X-party, Datastorm
Music scene: SID files, new compositions
Hardware mods: Accelerators, RAM expansions, video upgrades

The C64 never died. It evolved.

Programmer Resources

Starting out:

BASIC V2 for learning fundamentals
POKE commands for hardware access
Type-in listings from books/magazines

Intermediate:

Direct screen/sprite POKEs for games
Embedded machine code (SYS calls)
Understanding memory map and banking

Advanced:

Pure assembly language development
Raster interrupts for split-screen effects
Custom character sets and bitmaps
SID music programming
Sprite multiplexing (>8 sprites on screen)

Tools:

Emulators: VICE (cross-platform), CCS64 (Windows)
Assemblers: KickAssembler, ACME, 64tass
Sprite editors: SpritePad, Spritemate
Music trackers: GoatTracker, SID Wizard
Debuggers: VICE monitor, C64 Debugger

The 8-bit every kid could afford