Commodore PC 20-II

Facts

  • Type: Personal computer
  • Manufacturer: Commodore
  • Released: 1985 EU (1987 USA)
  • OS: Commodore MS-DOS 2.11-3.2
  • CPU: Intel 8088 @ 4.77 MHz
  • Memory: 640 KB RAM (PC20-II)
  • Video: VGA (640 KB RAM)
  • Graphics: MDA, Hercules, CGA (config by DIP switches)
  • Audio: PC speaker (1 bit)
  • Internal storage: 20 MB 5.25″ MFM HDD (PC20-II)
  • Removable storage: 360KB 5.25″ FFD
  • FPU: Optional 8087
  • Expansion slots: 5 x ISA-8
  • Predecessor: Commodore CBM II-series
  • Successor: Commodore PC30/PC40

Released 1985: The Commodore PC20-II is a home/business desktop computer in the range of Commodore International’s IBM PC compatible line. It’s an IBM PC XT clone running at 4.77 MHz, it came with an 20 MB hard drive, and an 5.25″DD floppy disk-drive and 640 KB RAM (256 KB directly on motherboard and 384 KB on a proprietary RAM expansion card) and a socket for optional 8087 FPU. It also got the floppy-disk controller integrated on the motherboard.

Background history: In 1984 Commodore signed a deal with Intel to second source manufacture the Intel 8088 CPU used in the IBM PC. Commodore also abandoned their own business line of Computers, the CBM-II series in 1984. The CBM-II line in turn was released only two years earlier, in 1982 to replace the CBM/PET-series. The CBM-II series was made with an expansion port to expand with an optional Intel 8088 CPU card to run MS-DOS 2.1.  The Intel 8088 CPU card for CBM-II Series was never officially released or sold by Commodore, but working units produced by Commodore exist today.

Incompatible with their own Commodore 64/128 and Amiga architectures, they were generally regarded as good, serviceable workhorses with nothing special, but the established Commodore name was seen as a competitive asset. I personally remember Commodore PC clones being used in offices in the company where I worked during school vocations, so they were pretty common. Commodore became the third largest distributor of PC compatibles here in Norway, in addition to their other very successful lines of computers like the Commodore 64/128 and Amiga-family.

Commodore PC 10
Commodore PC 10 

My Commodore PC20-III

This Commodore PC model looks exactly like the PC my father borrowed home from his work at Christmas holidays and so on when me and my brother were kids in the late 80’s. We currently had a Commodore 64, but found it very exiting to try out games that existed on PC and not the C64 at home, like Sierra Online adventure games, Space Quest II, Police Quest and Leisure Suit Larry.

I’ve traded this computer for a spare Commodore CBM 3032 I’ve picked up in Sweden and restored. A friend had a two of these, and I had two CBM 3032’s.

The Commodore PC was working and in reasonable good shape already. The current owner had already installed a Intel 8087 FPU. The original MFM type 20 MB hard disk had failed though, and the power supply rocket switch to turn the computer on or off. A dip-switch on the motherboard had also failed, but a new replacement dip-switch to solder in came along with it. I’ve bought myself a de-solder station from Poland,  so it was not to much struggle to replace the dip-switch. I’ve then replaced the hard disk with a Lo-tech’s ISA XT CF Adapter I ordered and had to wait for to arrive. This is in short a card that lets a CF memory card be used as a hard disk, using an IDE-CF adapter in between. In the end I also replaced the failed power switch with another switch I had laying around. When I got the the CF-card setup right, the machine was working just like I hoped for.

Commodore PC20 - II running Space Quest II
Commodore PC20 – II running Space Quest II (CGA in monochrome)

Upgrades and repairs:

  • Replaced the on/off rocket switch with one unoriginal I had laying around.
  • Installed  ISA XT CF Adapter and a IDE-CF adapter to replace the failed MFM hard disk.
  • Replaced the 8088 CPU with a compatible NEC V20 CPU (maybe ~10% speed increase).
  • Replaced a failed dip-switch on motherboard for configuration settings.
Commodore PC20-II

Remi Jakobsen


I'm collecting classic computers and video games, stretching from the 70's into the 90's. Restoration, history, usage ...


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