Commodore  CBM B500
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Commodore CBM B500 - Overview

The Commodore CBM B500, was a similar computer to the P500, but for the business market. The VIC-II chip was replaced by a MOS 6545 CRT Controller, capable of 80 columns text. The SID Sound chip was not removed, but the two joystick ports were. Interestingly, the connectors do exist on the motherboard but the ports in the backside of the case have been removed in this model.

Commodore CBM 500 Series

The Commodore 500 series was introduced in 1982. They are very similar to the CBM 600 series computers, which were launched at about the same time. Memory ranged from 64KByte to 256KByte. There were three models:

  • Model 505 - 64KByte RAM (No documentation found about this machine)
  • Model P500 - 128KByte RAM for the professional market
  • Model B500 (CBM 510) - 128KByte RAM for the Business Market
  • Model B500 (CBM 520) - 256KByte RAM for the Business Market
The machines have 24KByte ROM, a IEEE-488 Bus, a dual 8-bit user port, a RS232C communications port. It also has a joystick port, accessible on the motherboard, but there is no hole in the case for it.

The CBM 500 series uses a lot of the same chips that the Commodore 64 uses are used in the 500 series:

  • VIC-II video chip - 320x200, 16 colors, 40 column text
  • SID 6581 Sound chip - 3 channel sound
The 500 series uses the MOS Technology 6509 CPU which is capable of addressing up to 1MByte of RAM where the C64 uses the MOS 6502 which can only address 64KByte. In the end, the 500 series did not get produced for the American market due to regulatory problems and the fact that the C64 was much cheaper to manufacture.


  • Extended Basic v4.0
  • 40x25 video mode in 16 colors (VIC-II)
  • 64/128/256 KByte memory
  • MOS 6509 CPU, Clocked at 1MHz
  • Built in machine language monitor
  • 2 joystick ports, user port & cartridge port
  • IEEE488 parallel connector, RS232C port

MOS 6509 CPU

THe MOS Technology 6509 is an enhanced version of the 8-bit 6502 CPU. Using bank switching the 6509 is able to address up to 1MByte of RAM. The 6502 also could do bank-switching, but did so via separate logic circuits, the 6509 had this logic built in. This extra logic made the 6509 difficult to program, and it was mainly used in the Commodore CBM-II line of computers.

Source:WikiPedia - MOS Technology 6509
Source:WikiPedia - MOS Technology 6502

SID (MOS 6581) - Sound Interface Device

SID is short for Sound Interface Device. It is the name of the sound chip that was used in the VC10, the commodore 64 and the Commodore 128. SID was developed by Bob Yannes, an employee of MOS Technology. Bob was not only an engineer but also knew a lot about music. His intention was to create a different sound chip than other devices at the time. He implemented a subtractive synthesis chip. The chip's distinctive sound is easily recognized and was clearly ahead of the ocmpitition. The SID combines analog and digital circuitry that cannot be 100% emulated, even today.

Source: C64 Wiki
Technical Details
Released 1982 Brand Commodore Type Commodore CBM-II 500 Series Name CBM B500 CPU Class 650x CPU MOS 6509 @1MHz Memory RAM: 128kB Sound Chip SID (MOS 6581) Sound 3 Voices, 9 octaves Display Chip MOS 6545 CRTC Display 40x25 Monochrome text Best Text 40x25 Best Color monochrome Best Graphics Text Only Sprites none System OS BASIC V4.0
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World Wide Web Links
WikiPedia: MOS Technology 6581
Wikipage about the 6581