A Brief History of CP/M on the Commodore 128 (C128)

[BillBuckels]

A Brief History of CP/M on the Commodore 128 (C128)

The following is a condensed and abridged summary of the history of CP/M on the C128. For the original article that this was condensed from visit the following (Canadian) link:

http://www.commodore.ca/products/128/Commodore_128.htm

In the summer of 1984 Commodore decided that they needed a replacement for the amazingly successful C64. Customer reaction to Commodore's failure to provide native CP/M support in the C64 taught Commodore engineers some hard lessons.

Bil Herd got the top job as 128 lead Engineer presumably because of his vocal criticism of the new management team's lack of vision. (Type SYS 32800,123,45,6 on a C128 and you will see an "Easter Egg" with small list of development credits. Note the spelling of the word Hardware as Herdware.)



Bil Herd stated that a number of "odd engineering fixes", often conceived after consuming a few beer at the bar beside the MOS factory, resulted in seemingly insurmountable problems being quickly resolved. The most important of these 'fixes' was the integration of a Z-80 CPU into the main board, which elevated the C128 into the realm of the business computer.

This new machine would act as three completely separate computers in one:

1. Commodore 128 Mode 2Mhz Speed (8502 CPU), 128K Memory, very nice 80x25 RGB display, advanced Basic 7.0

2. Commodore 64 Mode 1Mhz Speed (6510 emulation in the 8502 CPU), 99.8% compatible with 64 hardware and software, accessed by booting the machine while holding down the Commodore key or typing GO 64

3. Commodore CP/M Mode 1-4Mhz Speed (Zilog Z-80 CPU), 100% compatible with the huge volume of CP/M business applications such as WordStar (an excellent combination word processing and text editor program many of us used for years).  Note that the Z-80 processor was originally spec'd by Commodore management to be the same external expansion cartridge used on the C64.  However, to resolve several other engineering problems, Bil Herd designed the Z-80 into the main board. This mode required CP/M software disks to be loaded on boot up.

Von Ertwine (a consultant) was developing CP/M at home. Von had wisely chosen not to try to follow all of the current Revs of the 8563 Video Chip, instead he latched onto a somewhat working Rev4 and kept it for software development. To make the 8563 work properly, Von was taking the little metal butter cup that came with his hot air popcorn popper and would put an ice cube in it and set it on the 8563. He got about 1/2 hour of operation per cube

In January of 1985 when Von Ertwine tried to make his CP/M work with the other (newer) 8563 Video Chips on the C128 demo machines at the C128's premiere, the Consumer Electronics Show (CES), he was at first unable to do so. He had stopped upgrading 8563s on his development machine somewhere around Rev 4 and a problem (bug) had appeared somewhere around Rev 6. As Von didn't carry all the machinery to do a CPM rebuild to fix the bug in software, it looked like CPM might not be showable. One third of the booth's design and advertising was based on showing CPM.

In "TRUE Animal fashion" Von sat down with a disk editor and found every occurrence of bad writes to the 8563 and hand patched them. Bear in mind that CPM is stored with the bytes backwards in sectors that are stored themselves in reverse order. Also bear in mind that he could neither increase or decrease the number of instructions, he could only exchange them for different ones. He even hand calculated the new checksums for the sectors. All this with a Disk Editor.

Production of the C128 started in June 1985 and stopped in 1989.

In the End, the 128 went on to be a notable success for Commodore but not because of its new power.  Unfortunately most software developers ignored the new and advanced C128 Mode functionality.  Why develop software for a new, relatively small product like 128's native mode when you can write software for the wildly successful C64 and know that your code will function on a 128 operating in 64 mode?

On a sad note, the 128's CP/M Mode was almost never used because CP/M was quickly losing ground to Microsoft Disk Operating System (MS DOS) by then running at version 2.  MS-DOS was of course popularized by the IBM PC and seemingly endless line of IBM clone machines. Business developers had all but abandoned the old standby CP/M in favour of the new and  rapidly expanding DOS market.  The Commodore 128 was CP/M's last big play, but the 128 just did not have the market penetration to keep CP/M alive.

Some C128 CP/M Resources:

http://www.herne.com/cpm.htm

GEnie Commodore File Library C128 CPM

Bill Buckels
bbuckels@escape.ca
March 2008

[xlar54]

Interesting read... I wonder how hard it would have been to instead have the 128 run with an 8088 processor so it could run MS-DOS back then instead of CPM...?

[airship]

the 128 just did not have the market penetration to keep CP/M alive.

The C128 was the biggest selling CP/M computer of all time, at 2-3 million units. The problem was that hardly anyone used the CP/M mode.