Commodore 64

Announced at the Winter CES in January 1982 and on shelves that August, the Commodore 64 sold for $595 — less than half what comparable machines cost, because Commodore owned MOS Technology and fabricated its own chips. It became the best-selling single computer model ever made, on estimates ranging from 12.5 to 17 million units, and stayed in production until 1994.

What made it last was not the 64K in its name but the two custom chips beside the CPU. The VIC-II gave programmers hardware sprites, smooth scrolling and raster interrupts; the SID gave them a three-voice synthesiser with resonant filters, ring modulation and oscillator sync.

Neither idea was new — Atari’s 400 and 800 had player/missile graphics and the four-channel POKEY from 1979, and the TI-99/4A had a three-voice sound chip. What was new was the combination at the price, and the SID’s depth: a filter and an ADSR envelope per voice made it an instrument rather than a tone generator, which is why C64 music is still performed and the Atari’s mostly is not.

Fast facts

CPU: MOS 6510 at 1.0227 MHz (NTSC) or 0.9852 MHz (PAL) — a 6502 with an added 6-bit on-chip I/O port at $0000/$0001.
RAM: 64K, with ROM and I/O banked over it under software control.
Graphics: VIC-II (6567 NTSC / 6569 PAL). 320×200 hi-res or 160×200 multicolour, 40×25 text, 16 colours, eight 24×21 hardware sprites, smooth scrolling, collision detection, raster interrupts.
Colour RAM: a separate nybble-wide static RAM outside the main 64K, documented throughout the period literature as $D800–$DBE7 — 55296 to 56295, exactly the 1000 cells a 40×25 display needs, one per character position.
Sound: SID (6581, later 8580). Three oscillators, four waveforms, ADSR per voice, a multimode filter, ring modulation and oscillator sync, and a 4-bit master volume.
I/O: two CIA 6526s for keyboard, joysticks, timers and serial.
Storage: Datasette tape at roughly 37 usable bytes per second; the 1541 5.25″ floppy at 170K; cartridges.

The raster beam as a clock

The Spectrum’s defining constraint is spatial — two colours per cell. The C64’s is temporal. Everything ambitious on this machine is organised around where the electron beam is.

The VIC-II raises an interrupt when the beam reaches a chosen scanline, so a program can change registers mid-screen: a different background colour at line 100, a different character set halfway down, sprites reused further along. This is how a machine with eight sprites shows thirty — sprite multiplexing, rewriting a sprite’s position and pointer after the beam has passed it.

The cost is that the VIC-II and the CPU share one bus, and the split is far more lopsided than it sounds. A PAL scanline is 63 cycles (NTSC is 64 or 65, depending on the chip revision). On a badline the chip refills its 40-entry character-pointer latch, asserts BA, and takes up to 43 of those cycles, leaving the 6510 twenty.

Sprites cost 2 cycles each per line on top, plus a 3-cycle lead-in. So the budget on one line runs:

Line	Cycles left to the CPU
Display line, no sprites	~63
Display line, all 8 sprites	~44
Badline, no sprites	20
Badline, all 8 sprites	~1

Badlines fall every eighth line through the display window, but which eight is set by the vertical scroll register, so a program that scrolls moves its own badlines. Code that runs comfortably for seven lines stalls on the eighth. Anything cycle-critical has to know where they fall and work around them, or blank the screen and buy the cycles back.

Contemporary technical writing put the aggregate cost plainly. The Home Computer Advanced Course, walking readers through the VIC-II in 1984, worked out that the chip’s DMA “slows up the 6510 by as much as 15 to 20 per cent”, and warned that the resulting absences are unpredictable enough to break real-time work — recommending that the screen be blanked with POKE 53265,11 for the duration of tape I/O and restored with POKE 53265,27 afterwards. The cycle counting above is what that percentage is made of, and the workaround the entry describes was standard advice at the time rather than a later discovery.

That is the C64’s real lesson, and the one the curriculum teaches through: on this machine you are not writing code that runs fast, you are writing code that arrives on time.

Why it mattered

Price. Owning the chip fab let Commodore cut hard and fast: US dealers were advertising the C64 around $199 during 1983, a year after a $595 launch. It went into homes that would otherwise have had no computer at all.
Hardware you could reach. BASIC V2 shipped with no commands for sprites, sound or graphics — everything went through POKE. Criticised at the time, it meant C64 owners met hardware registers on day one, which is a large part of why so many of them became programmers.
A music culture. The SID gave composers a recognisable instrument rather than a bleep, and Rob Hubbard, Martin Galway, Ben Daglish and Jeroen Tel became names players knew by sight on a cassette inlay.
The demoscene. Cracking groups became demo groups, and the techniques they invented chasing the hardware’s limits — raster splits, FLI, opening the borders — are still being extended today.
Longevity. Twelve years in production, and a software scene that has never stopped — new commercial and homebrew titles still ship on cartridge, disk and tape.

Models and variants

C64 “breadbin” (1982) — the original beige wedge.
SX-64 (1984) — a 10 kg luggable with a built-in 5″ colour monitor and 1541 drive, shown in 1983 and sold in volume from 1984. Generally credited as the first commercial portable computer with a full-colour display.
C64C (1986) — restyled to match the C128. Early units kept the long motherboard and the 6581 SID; the later short board brought the 8580, whose filter sounds audibly different. Which SID a given C64C has is a board-revision question, not a model one.
C64GS (1990) — a cartridge-only games console. It sold poorly; the C64’s library assumed a keyboard.

Quirks worth knowing

The 1541 is slow by design. The IEC serial bus is a slow, half-duplex, bit-banged design, and a stock load takes a minute or two. Nearly every commercial release shipped its own fastloader, replacing the drive’s transfer routine to cut that to seconds — a rare case of an entire industry routing around one component.
Tape is slower still. Native cassette throughput is about 37 bytes per second. Turbo loaders lifted that to 1,500–3,000, which is why the tape era survived at all.
Two colours per character cell, as on the Spectrum — multicolour mode buys a third and fourth at half the horizontal resolution. Sprites carry their own colours, which is part of why they do so much work in C64 games.

Modern legacy

Emulation: VICE is the cross-platform standard; MiSTer offers an FPGA recreation at hardware level.
Hardware: the Ultimate 64 replaces the motherboard with an FPGA; the 1541 Ultimate II+ replaces the drive with an SD card; MEGA65 extends the lineage rather than copying it.
Community: demo parties — Datastorm, X, Revision — still premiere C64 productions each year.

The 8-bit every kid could afford