1980s Vintage Computers

CP/M Computers

NorthStar Advantage

Digital Research CP/M was the dominant operating system for personal computers aimed at business users from the late 1970s  through to the mid 1980s. The machines usually had only floppy disks due to the high cost of hard drives at the time. Later there were a few portable machines that ran a version of CP/M from ROM. The market grew from its origins in the mid-70s due to the increasing range of off-the-shelf software packages as well as development tools such as various computer language compilers and interpreters. This benefited both manufacturers (who had less to develop to provide a working machine)  and the user (who could pick-and-choose from a range of vendors and transfer skills more easily). CP/M was the dominant OS for business use until the growth of the IBM PC and DOS, which pre-Windows was not all that different to CP/M from a users view point.

The early CP/M machines used an Intel 8080 processor (which  later was developed into the 8085), or the faster Zilog Z80 processor. Both of these had an 8-bit data bus and 16-bit address bus, giving a maximum addressable memory size (without using paging) of 64K bytes. Clock speeds generally ranged from 1MHz to 4MHz, and for tasks such as word processing or accounts they gave good performance. Typical CP/M machines used the S-100 bus, and would have separate cards for the processor, RAM, disk controller and I/O. With the advent of the 16-bit 8086 CP/M evolved into CP/M-86, and there were also  versions for the 16-bit 68000, but these were not as popular as the 8-bit versions. The early CP/M machines were text only (typically with a dumb terminal connected to a processor unit). Later machines introduced graphics, but initially manufactures had to provide their own non-standard extensions to CP/M and graphics performance could be poor. This was resolved once Digital Research produced the GEM graphics environment. 

CP/M was not perfect however, a typical drawback was that  disks could not usually be swapped between one CP/M machine and another due to differences in the floppy format (this was a common problem until DOS became dominant). There were two ways around this, either to link two different CP/M machines and perform file transfers or to have a dedicated disk copying machine that supported multiple disk formats.

The following shows my collection of CP/M machines (in approximate date order), and gives an impression of the variety especially towards the final years of CP/M: Please click on the links on the left for a more detailed page on a few machines.

Cromemco Z-2D
Transam Tuscan
Merlin M2215
Pericom 7800
NorthStar Advantage
Osbourne 1
Research Machines 380Z
Zenith Z-120
DEC Rainbow 100
Amstrad PCW-256

The Cromemco Z2 was introduced in 1979 but remained in use for several years due to its very rugged construction and huge 21-slot S-100 bus. My machine is a Z-2D so has twin 5" floppy drives. It came to me with an ADM-3A dumb terminal, but currently it only runs CDOS not CP/M.

The Transam Tuscan S100 was a British made microcomputer, launched in 1981. It was sold in a range of systems starting from a kit of parts based on a motherboard, up to a complete system with floppy and hard disks. It had a Z80 processor and RAM on a motherboard, which also had eight S-100 bus slots for expansion. The cased version had a built in keyboard and drove a text-only monitor directly.  My machine has twin 5" floppy drives, but does not currently boot up. These machines are now incredibly rare, if you have either a Tuscan (or the earlier Triton) or know where one is please e-mail me to help preserve their history.

The Merlin M2215 was made by ICL in around 1982 as the DRS 20 (here is the similar looking ICL Quattro) and re-badged as the Telecom Merlin. This was based largely on the earlier RAIR Black Box. It used a 8085 processor and I think it had a 50-pin bus. My model has twin 5" floppy drives and a dumb terminal, it powers up OK but I don't have a boot disk.

The Pericom 7800 was only produced in small volumes, and was based on a Pericom dumb terminal with a S-100 card cage integrated into the main case, a separate keyboard and a dual 8" floppy unit that acted as a monitor stand.  The machine is text-only, and my unit is in full working order.

The NorthStar Advantage (pictured at the start of this page) was unusual as it provided a high-resolution graphics display of 640x240. It used a motherboard approach based around a Z80 processor, 64K RAM, with a built in keyboard, floppy disk controller and graphic processor. Serial and parallel ports were available as plug-in cards on its custom bus. A 16-bit 8088 processor card was available as an upgrade. The machine came with a special graphics version of CP/M,  and also GDOS (Graphics DOS) and GBASIC which was NorthStar's custom operating system for this machine. This machine is fully working, I have NDOS, CP/M and the Demo / Diagnostic disks for it.

The Osbourne 1 was one of the first first portable CP/M computers available, and due to a successful marketing campaign became very popular. There are plenty of sites on the web on this machine, including full documentation.

Research Machines brought out the 380Z back in 1978 for the UK market. It came in a very plain black metal case, which was an off-the-shelf rack-mountable shelf. It came with a cassette interface and the option of floppy drives for CP/M support right from the beginning. It was built as a series of cards (joined by a ribbon cable bus)  that could be supplied according to the users needs. The most basic system was a Z80 / RAM / EPROM card plus a low-res graphics card, and up to 10 cards could be fitted in the case. RML developed the machine for about four years and then brought out a more sleek 480Z which offered backwards compatibility. This supported a network interface to allow CP/M to be loaded from a 380Z based server and run on the 480Z. This set-up was used in many schools in the UK in the mid-1980s.

The Zenith Z-120 was a popular machine in the US, and had a steady following through the 1980s and even the early 1990s. It featured a motherboard with dual 8085 and 8088 processors (to support 8-bit CP/M software and 16-bit MS-DOS software), 128K or more of RAM and also had the advantage of also featuring a S-100 bus. Most models supported a monochrome display, colour was also available as an option. The display supported graphics at a resolution of 640x225. My machine has a built in monochrome display. I have recently fixed it, and currently have MS-DOS 3.2 disks, but am looking for a CP/M boot disk.

DEC started out in the mini-computer business, and launched the Rainbow series around the same time as the IBM PC came out. Similar to the Zenith Z-100 series the Rainbow has a motherboard with dual processors, a Z80 and 8088, so CP/M is available in 8-bit mode and MS-DOS in 16-bit mode. It also has a built in emulator for the Digital VT-100 terminal.  It had very good graphics ability (up to 800x240). My Rainbow 100 has a dual 5.25" floppy unit, but the machine was given to me in a poor state and I have yet to test it.

Last up in my collection is the Amstrad PCW 8256. This machine was a huge success in the UK and in some other European countries like the Netherlands and West Germany, and over its lifetime the range sold over 200,000 units in the UK alone. It was supplied with  the Locoscript 1 word processor and CP/M 3, the final version of CP/M for the Z80. It was a budget machine and looked down on by computer professionals due to its cheap materials, 8-bit processor and lack of expansion slots at a time when 16-bit PCs such as the IBM AT and its clones were become the new standard. The PCW 8256 had a Z80  running at 3.4MHz, 256K RAM (as per the name), and two 3" floppies (another reason this machine is frowned upon, but at the time of launch 3.5" drives were not yet the norm). Unusually it came as a bundled system with a cheap but surprisingly reliable dot matrix printer, and good documentation.  Amstrad developed the PCW range which carved out a niche for serious home users and small businesses, and a large number of tried and tested CP/M software packages were available for it. The Locoscript word processor had a huge following, and was enhanced up to release 3, with features such as laser printer support. Companies such as Luxsoft still support the PCW range today! I now have two of these, both power up, one is fully working (once the floppy drive belt was replaced) and the other has some other fault with the  floppy drive.

As CP/M became dominant, other computer manufacturers produced add-ons for their machines to allow them to run it. Here is a summary:

Apple II - Microsoft produced the Softcard with a Z80 and ROM, but cleverly re-uses the Apple II's RAM to store CP/M OS and applications. 

HP-87 - HP produced the CP/M processor (a Z80 with 64K RAM) as a plug-in module, this allowed HP to port CP/M to the card and use the HP-87 as a dumb terminal to access it and also to allow the HP-87 floppy drive to be used. However the implementation was not very open, and only those applications provided by HP could be used.

BBC B - Acorn provided the Z80 second processor with its own RAM, and provided CP/M on floppy disk. The BBC B acted as a high-speed graphics terminal and floppy disk controller. This system was used quite widely, and a similar approach was used on the Torch computer.

Nascom 2 - As a Z80 machine this was ideal to be upgraded to allow CP/M to be run. A small hardware modification was needed to re-locate the boot ROM to the high end of memory though. 




This page was last revised on: 04/07/07