Conversational Monitor System

From Free net encyclopedia

Revision as of 01:34, 5 January 2006; view current revision
←Older revision | Newer revision→

The Conversational Monitor System (CMS) is a relatively simple interactive computing single-user operating system which was for many years IBM's principal time-sharing product. CMS runs primarily on IBM mainframe computers on top of the VM virtual machine operating system. Each CMS user appears to have their own personal operating system on their own private computer. The pair form a standard product, VM/CMS.

CMS provides users an environment for running applications or batch jobs, manage data files, create and debug applications, and communicate with other systems or users.

The acronym CMS originally stood for Cambridge Monitor System, after the IBM laboratory (the Cambridge Scientific Center) where it was developed; it was later renamed by IBM when VM/370 became an official IBM product in 1972.

CMS was developed in concert with VM to provide a time-sharing system; its original form was heavily influenced by CTSS, which was built by people at the same location (at MIT) as CSC. CTSS was actually used to develop initial versions of CMS software, using cross assemblers.

Users log in to VM, providing a userid and password, and then boot their own virtual machine. This is done by issuing the command 'IPL CMS' ("IPL" stands for "initial program load"; standard IBM jargon for booting a machine), though this is normally done automatically for the user. Personal customization is done by a standard shell script file named 'PROFILE EXEC', which sets up user-specified environmental defaults, such as which disks and libraries are accessed.

While CMS started in the era of paper line terminals, by the late '1970s most users were connecting with full-screen terminals such as the IBM 3270. Unlike dumb terminals, they have local buffer storage and minimal processing abilities to deal with an entire screen of information at a time. The terminal deals with information in its buffer during editing. This enhances overall system performance because the mainframe doesn't have to deal with every keystroke typed by a user; the entire set of updated screen fields is transmitted to the mainframe when the ENTER key or a program function key is pressed.

CMS garnered a very good reputation for being efficient and having good human factors for ease of use, relative to the standards of the time and prior to "GUI" environments such as are commonly used today. It was not uncommon to have hundreds of concurrent CMS interactive users on the same VM mainframe, with sub-second response times for the most common, "trivial" functions. Users program in FORTRAN, PL/I, APL, or the scripting language REXX, or use commercial software packages such as SAS. At one time, CMS was a major environment for e-mail and office productivity, using the IBM product PROFS, which was later renamed OfficeVision.

Two of the commonly used CMS tools include the editor XEDIT and the REXX programming language. Both of these products have been ported to other platforms and are now widely used outside the mainframe environment.

CMS is still in development and wide use today.

[edit]