KB10009: Commodore 8-Bit Models Compared – PET to C128

Commodore produced one of the broadest ranges of 8-bit home computers in the industry, spanning from 1977 to the early 1990s. The lineup includes the business-oriented PET series, the breakthrough VIC-20 and Commodore 64, the ill-fated 264 series, and the versatile C128. This article covers every major model, what changed between them, and what matters for collectors and restorers today.

Commodore PET / CBM Series (1977–1985)

The PET (Personal Electronic Transactor) was Commodore's first personal computer and one of the original "trinity" of 1977 alongside the Apple II and TRS-80. The original PET 2001 shipped with a MOS 6502 processor at 1 MHz, either 4 KB or 8 KB of RAM, a built-in cassette deck, a tiny chiclet keyboard, and a built-in 9-inch green monochrome monitor. It ran Commodore BASIC (licensed from Microsoft) from ROM.

PET 2001 Revisions

The earliest 2001 units had the infamous chiclet keyboard, which was widely criticized. Commodore quickly moved to a full-travel keyboard. The 2001-N ("New") series featured a proper keyboard, separated the cassette deck into an external peripheral, and offered 8 KB, 16 KB, or 32 KB of RAM. The display was a 40-column by 25-line monochrome screen using the PETSCII character set.

CBM 3000 / 4000 / 8000 Series

These were incremental upgrades for the business and education markets. The 4000 series (4016, 4032) offered 40-column displays with 16 KB or 32 KB of RAM. The 8000 series (8032, 8096) stepped up to an 80-column display, making them more practical for business use. The 8096 added 96 KB of RAM through bank switching. The SuperPET (SP9000) included a Motorola 6809 co-processor and offered programming languages like APL, FORTRAN, and Pascal alongside BASIC. All PET/CBM models used the IEEE-488 bus for peripherals, which was robust but expensive compared to the serial bus used in later Commodore machines.

Commodore VIC-20 (1981)

The VIC-20 was Commodore's first true mass-market home computer and the first microcomputer to sell one million units. It used the MOS 6502 processor at approximately 1 MHz with just 5 KB of RAM (3.5 KB available to BASIC). The VIC (Video Interface Chip, MOS 6560/6561) provided 176×184 pixel resolution with a fixed character display of 22 columns by 23 rows and a palette of 16 colors. Sound came from the VIC chip as well, offering three square-wave voices plus a noise channel. The VIC-20 introduced Commodore's IEC serial bus for disk drives and printers, which would carry forward to the C64 and C128. It had a single cartridge port, a user port, and an expansion port. Memory could be expanded via cartridge to 32 KB or more. The machine retailed for under $300 and was sold in mass-market retail stores, a first for home computers.

Commodore 64 (1982)

The Commodore 64 became the best-selling single personal computer model of all time, with estimates of 12.5 to 17 million units sold. It was built around the MOS 6510 CPU (a variant of the 6502 with an integrated I/O port) running at approximately 1 MHz, paired with 64 KB of RAM—an extraordinary amount for a sub-$600 machine in 1982.

VIC-II Graphics

The MOS 6567/6569 VIC-II (Video Interface Controller II) delivered 320×200 high-resolution graphics or 160×200 multicolor mode, with 16 colors, hardware sprites (8 independently movable objects), and smooth hardware scrolling. This was a major leap from the VIC-20's capabilities and made the C64 a formidable gaming platform.

SID Sound

The MOS 6581 SID (Sound Interface Device) chip, designed by Bob Yannes, was one of the most advanced sound chips in any home computer. It provided three independent oscillators, each capable of four waveforms (triangle, sawtooth, pulse with variable width, and noise), a programmable multi-mode filter (low-pass, high-pass, band-pass, and notch), ring modulation, and oscillator synchronization. The SID gave the C64 audio capabilities that rivaled dedicated synthesizers and spawned an entire demoscene music culture.

C64 Revisions

The original "breadbin" C64 went through several board revisions internally, gradually consolidating chips and reducing manufacturing costs. The most notable external revision was the C64C (1986), which featured a redesigned, slimmer case matching the C128's aesthetics. Internally, the C64C used a cost-reduced motherboard and the newer MOS 8580 SID chip, which had slightly different filter characteristics from the original 6581—a difference that audio enthusiasts and demoscene programmers consider significant. Some later C64C units used a combined "SuperPLA" chip to further reduce component count.

SX-64

The SX-64 (1984) was a portable version of the C64 with a built-in 5-inch color CRT monitor and a 1541-compatible floppy drive in a luggable case. It weighed about 23 pounds. Functionally identical to a standard C64, its main collector interest is the compact form factor and built-in display. It was one of the first portable computers with a color screen.

264 Series: C16, C116, and Plus/4 (1984)

Commodore's 264 series was intended to segment the market—the Plus/4 as a low-cost business machine and the C16/C116 as a budget VIC-20 replacement. Unfortunately, the series was not software-compatible with the enormously popular C64, which severely limited its adoption.

All 264-series machines used the MOS 7501 or 8501 CPU (a 6502 variant) clocked at approximately 1.76 MHz—roughly 75% faster than the C64. The TED (Text Editing Device, MOS 7360/8360) chip handled both video and sound, producing 320×200 resolution with a palette of 121 colors (16 hues at 8 luminance levels, plus black). However, the TED's sound was a significant downgrade from the SID—only two channels with square and noise waveforms. The Plus/4 had 64 KB of RAM and included built-in productivity software (word processor, spreadsheet, database, and graphing tool) in ROM. The C16 had only 16 KB of RAM. The C116 was essentially a C16 in a smaller case with a rubber keyboard, sold primarily in Europe. None of these machines had a SID chip, sprites, or the C64's user port, making them incompatible with C64 peripherals and software.

Commodore 128 (1985)

The C128 was Commodore's most versatile 8-bit machine, designed from the ground up to run in three distinct operating modes.

C64 Mode

Full hardware-level Commodore 64 compatibility. The machine physically reconfigured itself to match a C64, running the same ROMs with the same VIC-II and SID chips. Nearly all C64 software ran without modification.

C128 Mode

Native mode with the MOS 8502 CPU (an enhanced 6510 variant) running at 1 or 2 MHz, 128 KB of RAM arranged as two 64 KB banks, BASIC 7.0 with built-in graphics and sound commands, and an 80-column display driven by the MOS 8563 VDC (Video Display Controller) chip. The VDC provided 640×200 monochrome or 640×200 with 16 colors from the palette, using its own dedicated 16 KB of video RAM (upgradable to 64 KB). The 40-column display still used the VIC-IIe chip, maintaining C64-compatible graphics capabilities.

CP/M Mode

A built-in Zilog Z80 co-processor running at 4 MHz allowed the C128 to boot CP/M 3.0 (CP/M Plus), giving access to a vast library of CP/M business software. This was a carryover from the C128's original design goals to appeal to the business market.

C128D and C128DCR

The C128D was a desktop version with a detached keyboard and built-in 1571 double-sided floppy drive. The C128DCR ("Cost Reduced") was a later revision that replaced many discrete chips with a single custom MOS chip, reduced the board size, and used a metal case instead of plastic. The DCR is generally considered more reliable due to its simplified design.

Quick Comparison Table

Model	Year	CPU	Speed	RAM	Graphics Chip	Sound Chip
PET 2001	1977	6502	1 MHz	4–8 KB	Built-in (monochrome)	Piezo speaker
CBM 8032	1980	6502	1 MHz	32 KB	Built-in (80-col mono)	Piezo speaker
VIC-20	1981	6502	1 MHz	5 KB	VIC 6560/6561	VIC (3 voice + noise)
C64	1982	6510	1 MHz	64 KB	VIC-II 6567/6569	SID 6581
C64C	1986	6510	1 MHz	64 KB	VIC-II 8562/8565	SID 8580
SX-64	1984	6510	1 MHz	64 KB	VIC-II	SID 6581
Plus/4	1984	7501/8501	1.76 MHz	64 KB	TED 7360/8360	TED (2 channel)
C16	1984	7501/8501	1.76 MHz	16 KB	TED 7360/8360	TED (2 channel)
C128	1985	8502 + Z80	1–2 MHz	128 KB	VIC-IIe + VDC 8563	SID 6581/8580

Collector and Restoration Notes

PET units often have power supply issues and aging CRTs. On the VIC-20 and C64, the most common failure point is the original power supply—the "brick" supply can deliver excessive voltage and damage the machine. Always test or replace the power supply before powering up an untested unit. The SID and VIC-II chips are susceptible to damage from power surges and are increasingly difficult to source. On C64C and C128 units, the later 8580 SID has different filter behavior than the original 6581, which matters for music and demo playback. C128 VDC chips can fail, and the 1571 drive in the C128D may need head alignment or belt replacement.