CP/M

CP/M is an operating system created for Intel 8080/85 and Zilog Z80 based microcomputers by Gary Kildall of Digital Research, Inc.

History

The beginning and CP/M's heyday

For a time after December 1974, the date of first use of CP/M, Control Program/Monitor was what CP/M stood for. This ended some time prior to 15 November 1976, the date of first use of the mark CP/M in commerce. By the time that CP/M was a mark in commercial use, CP/M stood for Control Program for Microcomputers. These dates are recorded in trademark registration number 1112646 serial number 73149955 at the United States Patent Office as filed by Intergalactic Digital Research, Inc. doing business as Digital Research Corporation on 25 November 1977 by an attorney acting on behalf of Gary Kildall himself. This renaming of CP/M was part of a larger effort by Kildall and his business-partner wife to convert Kildall's personal project of CP/M and the Intel-contracted PL/M compiler into an ever-more-serious commercial enterprise, where "micro", as in microcomputer, was a consistent branding, including not only Control Program for Microcomputers and Programming Language for Microcomputers but also a few years later Digital Research's Microport Unix that competed against Microsoft's Xenix. The Kildalls astutely intended to establish the Digital Research brand and its product lines as synonymous with "microcomputer" in the consumer's mind, similar to what IBM and Microsoft together later successfully accomplished in making "personal computer" synonymous with IBM and Microsoft product offerings. As further evidence that the renaming of CP/M in word form was part of a larger effort of keeping the CP/M and Digital Research Corporation brands stable in the public's mind while evolving the underlying business behind the scenes, the Kildalls effectively publicly renamed Intergalactic Digital Research, Inc. for use in commercial activities, via only a doing-business-as filing, to Digital Research Corporation. Intergalactic Digital Research, Inc. was later renamed via a corporation change-of-name filing to Digital Research, Inc., which itself continued to do business publicly as Digital Research Corporation for a time into the 1980s, after which Digital Research, Inc. did business under its own name.

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CP/M was originally distributed on 8 inch floppy disks, and ran on the Intel 8080 CPU (as well as the compatible and very popular Zilog Z80). Eventually, the industry moved to the 5¼ inch disk format, and CP/M followed -- however many companies developed their own, incompatible 5¼ inch disk formats, which made the exchange of disks between different CP/M-systems difficult in practice. Popular CP/M systems sometimes supported at least one other disk format than their own native format. Translation programs existed to allow interchange of files between disk formats.

Related Topics:
Floppy disk - Intel 8080 - CPU - Zilog Z80

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IBM never used CP/M in any of their computers, nor was there any other company with the domination of the market that IBM was to have in the early 1980s. This is the reason that there was such diversity of 5" disk formats under CP/M. A software manufacturer had to prepare a separate version of the program for each brand of hardware on which it was to run. With some manufacturers (Kaypro is an example), there was not even standardization across the company's different models. Because of this situation, disk format translation programs which allowed a machine to read many different formats became popular and reduced the confusion. With MS/DOS having a standard 5" disk format, a publisher could prepare one version of the program with the confidence that machines from different manufacturers could use it, at least with basic character mode video, because custom video graphics were still the norm until the introduction of IBM's EGA graphics with the model AT.

Related Topics:
1980s - EGA - AT

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CP/M was described as a "software bus", allowing multiple programs to interact with different hardware in a standardized way. Programs written for CP/M were typically portable between different machines, usually only requiring specification of the escape sequence for control of the screen and printer. This portability made CP/M popular, and much more software was written for CP/M than for operating systems that only ran on one brand of hardware. One restriction on portability was that certain programs used the extended instruction set of the Z80 processor and would not operate on an 8080 or 8085 processor.

Related Topics:
Escape sequence - Screen

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Hundreds of different brands of machines ran CP/M, some notable examples being the above-mentioned Altair, the IMSAI 8080, the Osborne 1 and Kaypro portables, and even the Apple II when an extra Z80-card was installed. The best selling CP/M capable system of all time was probably the Commodore 128, although few people actually used its CP/M abilities. In the UK, CP/M was also available for the BBC Micro— which could also be equipped with a Z80 co-processor. Furthermore, it powered the popular Amstrad PCW word-processing system.

Related Topics:
IMSAI 8080 - Osborne 1 - Kaypro - Apple II - Commodore 128 - BBC Micro - Amstrad PCW

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WordStar, one of the first widely used word processors, and dBASE, the first widely-popular database program for small computers, were originally written for CP/M.

Related Topics:
WordStar - Word processor - DBASE

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The 16-bit world

Versions of CP/M were later completed for some 16-bit CPUs as well, although they required the application programs to be re-compiled for the new CPUs -- or, if they were written in assembly language, to be largely rewritten from scratch.

Related Topics:
16-bit - Assembly language

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One of the first was CP/M-86 for the Intel 8086, which was soon followed by CP/M-68k for the Motorola 68000. At this point the original 8-bit CP/M became known as CP/M-80 to avoid confusion.

Related Topics:
Intel 8086 - Motorola 68000 - 8-bit

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CP/M-68k was widely used only in one application: it formed the basis of the Atari ST computer. CP/M-86 had the potential of becoming the standard operating system of the new IBM PCs, but minor legal issues made IBM turn to Microsoft instead. Microsoft purchased a CP/M clone known as QDOS, and used it to create PC-DOS/MS-DOS which went on to become the "official" PC operating system. CP/M-86 never became popular.

Related Topics:
Atari ST - IBM PC - Microsoft - QDOS - PC-DOS - MS-DOS

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MS-DOS takes over

Many of the basic concepts and internal mechanisms of early versions of MS-DOS were patterned after those of CP/M. Internals like file-handling data structures were identical, and both referred to disk drives with a letter (A:, B:, etc.). The main innovation was MS-DOS's FAT file system. This intentional similarity made it easier to port popular CP/M software like WordStar and dBase. However, CP/M's concept of separate user areas for files on the same disk was never ported to MS-DOS. Since MS DOS had access to more memory, more commands were built-in, most usefully the file COPY command. This made the command-line user interface of MS-DOS somewhat easier to use.

Related Topics:
FAT - File system - User interface

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CP/M rapidly lost market share as the microcomputing world moved to the PC platform, and it never regained its former popularity. Byte Magazine, at the time one of the leading industry magazines for microcomputers, essentially ceased coverage of CP/M products within a couple of years of the introduction of the IBM PC. For example, in 1983 there were still a few advertisements for S100 boards and articles on CP/M software, but by 1987 these were no longer found in the magazine.

Related Topics:
Byte Magazine - 1983 - 1987

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Later versions of CP/M-86 made significant strides in terms of performance and usability however, and for some time in the 1980s was considered to be a better x86 OS than MS-DOS. To reflect this compatibility the name was changed, and CP/M-86 became DOS Plus, which in turn became DR-DOS.

Related Topics:
DOS Plus - DR-DOS

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