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C C Executive and PSX (JMI Software Systems)
C EXECUTIVE is a operating system kernel for embedded applications - providing a small, efficient, real-time software environment for programs written in C. C EXECUTIVE, as small as 5 KB in ROM space, is available on 8-, 16- and 32-bit CISC and RISC processors, providing the foundation for a common, corporate-wide, portable software strategy. PSX provides a single-user, single-group, subset of POSIX.1, with up to 32,000 preconfigured processes. PSX adds a substantial subset of the POSIX.1 system calls to the basic C EXECUTIVE kernel. Using these calls allows applications to migrate from POSIX-conformant UNIX platforms to board-level systems, or vice versa.


Cache kernel (Stanford University Distributed Systems Group)
Group Members: David Cheriton, Kenneth Duda
The supervisor-mode component of the V++ operating system. The Cache Kernel caches operating system objects such as threads and address spaces just as conventional hardware caches memory data. User-mode application kernels handle the loading and write-back of these objects, implementing application-specific management policies and mechanisms.



A Cromenco CP/M compatible os. 


Chimera (Carnegie Mellon University)
The Advanced Manipulators Laboratory, at Carnegie Mellon University, has developed the Chimera Real-Time Operating System, a next generation multiprocessor real-time operating system (RTOS) designed especially to support the development of dynamically reconfigurable software for robotic and automation systems. Version 3.0 and later of the software is already being used by several institutions outside of Carnegie Mellon, including university, government, and industrial research labs.


Choices (University of Illinois, Urbana-Champaign)
Choices is written as an object-oriented operating system in C++. As an object-oriented operating system, its architecture is organized into frameworks of objects that are hierarchically classified by function and performance. The operating system is customized by replacing subframeworks and objects. The application interface is a collection of kernel objects exported through the application/kernel protection layer. Kernel and application objects are examined through application browsers


Chorus  Chorus (Sun Microsystems)
CHORUS is a family of open micro-kernel-based operating system components to meet advanced distributed computing needs in areas such as telecommunications, internetworking, embedded systems, realtime, "mainframe UNIX", supercomputing and high availability. The CHORUS/MiX multiserver implementations of UNIX allow to dynamically integrate part or all of standard UNIX functionalities and services in the\ above application areas.
A micro-kernel-based distributed OS.
Chorus Systemes has special programmes for universities interested in using Chorus. For more information on the offerings available, conditions, and other details, get the following files: 

(-> Tanenbaum, "Distributed Operating Systems") 
(Concurrent Computing Parallel OS


ConvexOS  (outdated)
Runs on Convex C 38xx Serie Computers.



CORBA (Common Object Request Broker Architecture) 
An architecture designed to enable programs on dissimilar platforms to exchange objects. The CORBA specification defines a standard interface between compliant objects. 
     Both the Gnome and KDE desktops for Linux and other Unix-like OSs have CORBA-based object architectures, with Gnome pushing the concept to its limits. 

The Distributed Systems Technology Center (DSTC) offers a range of commerical quality implementations of standardised CORBA services:  DSTC Object Trader   DSTC Meta Object Facility  DSTC Notification Service  DSTC Naming Service 


Cosy (Concurrent Operating Systems) 

(University of Karlsruhe, University of Paderborn)
Group Members: Wolfgang Burke, Roger Butenuth, Sven Gilles
Cosy is an operating system for highly parallel computers, with hundreds or thousands of processors. All parts of the system are designed to scale up with the number of processors, without any one becoming a bottleneck. . 

Cosy is a new operating system specifically designed for scalability of highly parallel multicomputer systems. It rests on a small microkernel responsible for process management and interprocess communication. All other OS services (e.g. file system, window system, name service, ..) are implemented as processes outside the kernel. In Cosy, processes and address spaces are orthogonal concepts which makes a Cosy process similar to a thread in other operating systems. 

Cosy is joint development of the Institute for Operating Systems and Interactive Systems of the University of Karlsruhe and the Institute for Operating Systems and Distributed Systems  of the  University of  Paderborn. 


CP/M (Control Program for / Microcomputers / for Microprocessors or /Monitor)  (outdated)
Official Homepage # Go to the OpenDos page, then select CP/M downloads. 

1973 developped by Gary Kildall. At that time only a simple monitor, which later through the introduction of the "bios" could handle floppy disks. First introduction to market 1975. CP/M established the first quasi-standard for micros of the 8080/Z80 variant(later also for 8086). It was considered as a semi-professional system by that time with a huge software-basis. All sorts of programs where available for CP/M: Compiler for all known computer-languages (and for all unknown languages), data-base systems in all variants, all text-processing software which later found there prolongation on MSDOS/Windows. But CP/M also had its weeknesses which let to the developpment of more competitive Operating Systems like TurboDos(1979), RTS-80(1980), to name just a few.

CP/M reached at its culmination point (around 1985) 500.000 official installations. But estimations spoke of 4 million installations world-wide, compatible systems included. Since the IBM-PC (and its taiwanese clones) with its 8088, later 8086 and 80186 were at the time of there introduction much slower than most CP/M systems, CP/M-users didn't changed their systems til the advent of the 80286(the CPU which was able to switch into protected mode but not back again!). But the real change-over took place with the 80386 which was the first Intel-Cpu which could not only switch into virtual mode but also back again.

The success of MSDOS (and thereby the decay of CP/M with its derivatives) in the long run was on one hand due to a false decission at ZILOG, they decided to give the Z8000 high priority instead of introducing the Z280 at its due deadline. This would have made possible a smooth upgrade. On the other hand the three blue letters helped to bring the MSDOS-PC's more and more sales. Most people had no possibilty for cross validation- so they decided for the three blue letters. But the ultimate succes was due to the taiwaneese clones, which sold for less than 1/5-1/3 the price of US- or european systems. Even at wholesale prices you couldn't even get the parts for that price in europe or in the US!

Gary Kildall couldn't get an employment at Intel, so he worked as a consultant for INTEL. (Intel had its own Operating-System, see ISIS)  His main work was beeing a teacher for computer science at the army school . Intel donated him a development system, which Gary used to write a PL/1 compiler. His disk-IO routines let later to the 'CONTROL PROGRAM for MIKROCOMPUTER'. Although the directory structure was by no means optimal, it was sufficient and quick. But the main reason for the success of CP/M did lay in his seperated 'Basic-Input-Output-System', short BIOS. Since the 'BASIC-IO-System' formed a seperate part, it was easy to adapt CP/M to all sorts of different hardware. This was the main reason for the success of CP/M. Running on machines such as Zenith, Kaypro, Osborne, Xerox, Vector Graphics, NorthStar, IMSAI, Commodore, Amstrad, Sharp and Starlet. Running such legendary software as WordStar. Personal computer pioneer Gary Kildall, who but for a single failed business deal might have enjoyed the wealth and fame of Bill Gates, died July 11, 1994, in a Monterey hospital at age 52. DRI was bought out by Novell and subsequently sold off to Caldera, which currently owns the copyright to all DRI software. On Sept 10, 1996, Caldera released all of the source code for DR products. 
     There have been lots of greatly improved clones, including ZCPR3 for the command processor and several replacements for the BDOS.  Some of these are commercial (e.g., ZSDOS/ZDDOS), but many have been released to the public. None of them has any comercial importance. Most of the latter can be obtained from and many BBSs. 
     There is also a CP/M-Plus replacement named ZPM3, written by Simeon Cran. It offers much more performance and some additional features compared to CP/M-Plus. An extended CCP, the ZCCP, is also available. Unfortunately, it still seems to have some bugs.  ZPM3 and ZCCP are free! However no sources as Simeon won't give them away. 
     Currently, the following CP/M computers are available: The YASBEC (uses a 64180, has  SCSI interface), which uses a proprietary bus system.The CPU280 (uses a Z280, an IDE interface is available), which uses the ECB-bus which allows many other I/O cards to be connected. The
PalmTech CPUZ180, designed and built in Australia. The complete SBC fits on a 6"x4" and runs at 18MHz. Included are floppy and IDE hard disk controllers, color/monichrome video controller, IBM PC/XT keyboard interface, printer parallel port, two serial ports, real time clock, 1 Meg ram, amd many other features. And the P112 from D-X Designs Pty Ltd is a single board CP/M compatible computer with the footprint of a 3.5" floppy disk drive. It provides a Z80182 (Z-80 upgrade) CPU with up to 1 MB of memory, serial parallel and diskette IO, and realtime clock in a 3.5-inch drive form factor.  Powered solely from 5V, it draws 150mA (nominal:  not including disk drives) with a 16MHz CPU clock. 
     Unlike today's computers where a BIOS is in ROM, the CP/M BIOS gets loaded off the boot floppy and lives in RAM. 
     For info on disk format, conversions and emulators see

Later versions like CP/m86, CCP/M86 had no success.

Publications  CP/M-FAQ maintained by Donald.C.Kirkpatrick <> Z80 Support Home Page maintained by Thomas Scherrer <> The Computer Journal (TCJ) 
LISTSERV@VM.ITS.RPI.EDU with "SUBSCRIBE CPM-L your full name" in the body of the message. comp.os.cpm
 Software - "abandoned" commercial software
simtel/msdos/emulator/ - ZSIM is an (extremely accurate) Z80 emulator (80386/40 -8 MHz Z80), free for personal use.  Sources of the CP/M BIOS are included. 


The Cronus object-oriented distributed system may be obtained via ftp from; email <> for details of the account name and password. Before attempting to get the Cronus distribution, you must obtain, via anonymous ftp, Maintenance, hotline support, and training for Cronus are available from BBN. Send email to the above address for information on these, or on obtaining a commercial license. 


CTSS (Compatible Time Sharing System)  (outdated)
2 Systems at MIT for a IBM 7084. One of the first systems with password-protected access. Experience with CTSS: "Most striking ist the way the users have built on one another's work... More than half of the commands now written into the system were developed by the users.. The users have very generally chosen to link up with one another's private files and the public files. Whereas in conventional computer installations one hardly ever makes use of a program develped by another user, because of the difficulty of exchanging programs and data, here the ease of exchange has encouraged investigators to design their programs with an eye to possible use by other people. They have acted essentially as if they were writing papers to be published in technical journals... It is now easy to envision the use of the system for education or for real-time collaboration between the members of a research team... The coupling between such a utility and the community it serves is so strong that the community is actually a part of the system itself." [Fano/Corbato 1966, S. 136 ff.] 


All about OSs


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