Commodore CBM-II

Commodore CBM-II

Commodore CBM-II
Type Personal computer
Release date 1982 (1982)
Discontinued 1984 (1984)
Operating system Microsoft BASIC 4.0
CPU MOS Technology 6509 @ 1 or 2 MHz, Intel 8088 option
Memory 128 or 256 kB
Graphics VIC-II (320 × 200, 16 colors, sprites, raster interrupt) or 6545 CRTC
Sound SID 6581 (Osc, Wave, Filter, ADSR, Ring)
Connectivity RS-232, A/V, Digital tape, ROM cartridge, Audio minijack, Mains power, Parallel IEEE-488 Floppy/Printer

The Commodore CBM-II series is a short-lived range of 8-bit personal computers from Commodore Business Machines (CBM), released in 1982 and intended as a follow-on to the Commodore PET series.


  • Technical description 1
  • History 2
  • References 3
  • External links 4

Technical description

The CBM-II has two incarnations, the P series (P = personal, or, home use) and the B series (B = business use). The B series was available with a built-in monochrome monitor (hi-profile) with detached keyboard, and also as a single unit with built-in keyboard but no monitor (lo-profile). These machines are known as the "Porsche PETs" for their unique styling.[1]

The P series uses the VIC-II 40-column color video chip like the C64. It also includes two standard Atari-style joystick ports. The 6509 CPU runs at 1 MHz in the P series due to the use of the VIC-II chip.

The B series uses a 6545 CRTC video chip to give an 80-column "green screen" monochrome output more suitable for word processing and other business use than the VIC-II's 40-column display. Most models have the Motorola 68B45 installed which is a pin compatible variant rather than the MOS 6545A1 2 MHz part. On the B series the 6509 CPU runs at 2 MHz.

Features common to both the P and B series included an MOS Technology 6509 CPU, an enhanced version of the venerable 6502, that was capable of addressing up to 1 megabyte of RAM via bank switching (however, no CBM-II model came with more than 256 kilobytes of RAM, 1/4 megabyte). The sound chip is the 6581 SID, the same one that was used in the popular Commodore 64 (C64) but with some limitations as it was over-clocked to 2 MHz. Additionally, the CBM-II has an industry-standard RS-232 serial interface and an IEEE-488 parallel bus (for use by disk drives and printers) just like the PET/CBM series. The CBM-II's built-in operating system uses an enhanced version of CBM BASIC version 4.0.

An optional Intel 8088-based coprocessor board allows the CBM-II series to run CP/M-86 1.1 and MS-DOS 1.25; however, the computers were not IBM PC compatible and very little, if any, software taking advantage of this capability ever appeared. The coprocessor board only runs on high-profile machines due to power supply and mechanical spacing requirements.

A Commodore CBM 610, the European version of a Commodore B128
Connectors on the back of a CBM 610
Mainboard and power supply of a CBM 610

The production naming within the United States and Canada was the B128/B256 and CBM128-80/CBM 256-80 while in Europe they were known as the 600 and 700 series respectively (no "B" in front of the model number). The P machine was known worldwide as the 500 series. There are prototype models though such as the B500 (earlier B128 design) and B700 (earlier CBM 128-80/CBM 256-80 design) known to exist.


Due to the popularity of the C64, the P series was cancelled in the United States before it could be officially released; however, a few dealers who received preproduction units sold them. As these computers had not received approval from the Federal Communications Commission, this caused legal problems for Commodore. The units were recalled and destroyed, but a very small number exist today, in private collections. At least one model, the P500, was commercially released in Europe but only sold in small numbers.

The most common of the B series was the low-profile B128[1] (called the CBM 610 in Europe), which had 128 kilobytes of RAM. The B128 did not sell well, and ultimately Commodore's inventory was liquidated by Protecto Enterprises ("We Love Our Customers"), a large Commodore mail order dealer based in Chicago, Illinois.[2] The Protecto ads for the B128 bundle, including a dual disk drive, monitor and printer, appeared in various computer magazines for several years.

After discontinuing the CBM-II range, Commodore handed its documentation, schematics, and all other information over to CBUG, the Chicago B128 Users Group.

Among these materials was a prototype motherboard using an Intel 8088 processor, which hints at the possibility the line could have been made IBM compatible if production had continued.

CBUG went on to develop a library of software for the computers. Its library, however, paled in comparison to the large software libraries enjoyed by the C64 and Commodore VIC-20.

The rounded case design of the high profile CBM-II series would later be used in redesigned versions of the original PET/CBM computers, (such as the CBM8296) that the CBM-II line was designed to replace.


  1. ^ Commodore PET 200 at, accessed 25 August 2014
  2. ^ "Commodore B Series The Dusk of the Day". 
  1. ^ a Neither the CBM128-80 nor the B128 are to be confused with the very different and reasonably successful Commodore 128 (also known as CBM 128 and C128), Commodore's final 8-bit home/personal computer, released in 1985.
  2. ^ a The CBM-II, due to a quirk in the input, if you do the command "POKE 0,35" will lock everything, and all of the memory will be filled with 00's and FF's.

External links

  • The Commodore CBM-II page — By Steve Gray
  • The Commodore B-series page — By Edward Shockley
  • Under the Hood of the Commodore P500 — By Ullrich von Bassewitz
  • The Commodore 500, 600 and 700 Computers — By David Viner
  • Hires graphics-board — By Winfried Falkenhahn
  • Michau's CBM-II page — By Michał Pleban
  • - The Commodore CBM-II Page