CP/M (Command Processor for Microcomputers) was an operating system for Intel 8080/ 85 and Zilog Z80 based microcomputers. It was created by Digital Research, Inc. founded by Gary Kildall. The combination of CP/M and S-100 bus computers patterned on the MITS Altair was the first "industry standard", and was widely used through the late 1970s and into the mid-80s.1 Description: CCP, BDOS, BIOS
CP/M's command line interface, implemented in the CCP command control processor, was patterned after the operating systems from Digital Equipment, such as RSTS/E for the PDP-11.
Commands generally took the form of a keyword followed by a list of parameters separated by spaces or special characters.
The commands themselves would sometimes be somewhat obscure; for instance, the command to duplicate files was named PIP (Peripheral-Interchange-Program).
One key innovation in CP/M was the use of an abstraction layer that separated the operating system into two main parts.
The CCP translated user commands into a series of high-level instructions.
These instructions were then fed into the BDOS (Basic Disk Operating System), which provided functionality like "open file". Application programs would likewise talk to the BDOS.
The BDOS then translated these commands into a new series of lower-level instructions.
These were then fed into the BIOS (Basic I/O System), which contained the hardware-specific code that carried out the instructions from BDOS.
To illustrate the flow of commands, consider the PIP command mentioned earlier. When a PIP command was entered into the CCP it was broken down into a series of instructions for the BDOS, which would be similar to "locate the file named foo.txt, open it, create a new file named bar.txt...". The BDOS commands in turn were sent to the BIOS as a string of even simpler instructions, like "move the disk head to this sector, read raw data from sector..." etc.
The vast majority of the complexity in CP/M was isolated in the BDOS, and to a lesser extent, the CCP.
This meant that by porting the limited number of simple commands in the BIOS to a particular hardware platform, the entire OS would work.
This significantly reduced the development time needed to support new machines, and was one of the main reasons for CP/M's widespread use.
Today this sort of abstraction is common to most OSs, but at the time of CP/M's birth, OSs were typically intended to run on only one machine platform, and multilayer designs were considered unnecessary.
2 History
2.1 The beginning and CP/M's heyday
CP/M was originally distributed on 8 inch floppy diskA floppy disk is a data storage device that comprises a circular piece of thin, flexible (hence "floppy") magnetic storage medium encased in a square or rectangular plastic wallet. Floppy disks are read and written by a floppy disk drive or FDD not to bes, 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 -- unfortunately every company cooked up their own 5¼ inch disk formats, which made the exchange of disks between different CP/M-systems difficult in practice. Programs written for CP/M were typically completely portable amongst different machines with the same CPU; this made it popular, and much more software was written for CP/M than for operating systems that only ran on one brand of hardware.
Hundreds of different brands of machines ran CP/M, some notable examples being the above-mentioned Altair, the IMSAI 8080The IMSAI 8080 microcomputer, manufactured by IMS A ssociates, I nc. later renamed to IMSAI Manufacturing Corp. in 1976, was an early Intel 8080, S-100 bus based computer, compatible with its main competitor, the earlier MITS Altair 8800, by which it was, the Osborne 1The Osborne 1 created by Adam Osborne and released in April 1981, was the first portable "all-in-one" microcomputer. It weighed 23. 5 pounds (12 kg), cost US$1795 just over half the cost of a comparable computer from other manufacturers with comparable fe and KayproKaypro was a manufacturer of CP/M compatible, portable1 microcomputers. Their first model was launched in 1982, and was built around the Zilog Z80 microprocessor—like the portable, CP/M-running Osborne 1 of 1981, Kaypro's "source of inspiration". The Kayp portables, and even the Apple IIpersonal computers of the 1980s. As can be seen, the Apple II came with an integrated keyboard, common with early personal computers, but very uncommon today. The one pictured is shown with two official Apple floppy disk drives and a monitor. The Apple II when an extra Z80-card was installed. The best-selling CP/M system of all time was probably the Commodore 128, although few people actually used its CP/M capabilities.
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.
