??! *.7~; .i CP/M: A Family of 8- .k&9 " G~, and 16-Bit-1 ,- P.Operating ." Systems -kvaka .& ' Dr Gary Kildall ',% Digital Research 4 ! I;- POB 579 .t 801 Lighthouse Ave +: Pacific Grove CA 93950 I' This article is about microproces- low-cost storage medium was paper management can be separated from ere they came tape (used in applications ranging the I/O (input/output) system (which t they are, and what from program development to word is not required in many applications). to be. Where they came processing). At a cost of $5, a floppy Real-time facilities allow the execu- , what they are today disk held as much data as two hun- tion of interactive processes accord- t they will become is, dred feet of paper tape, and a disk ing to priority, and their addition or tion of technology, drive retailed for only $500-an un- deletion in a simple fashion. This iction" speculation. beatable combination. Memory, pro- results in a custom operating system is an operating system devel- cessor, and floppydisk technology designed to solve a particular prob- microcomputers. But as improved, and by the mid-1970s, a lem. In contrast to timesharing, real- hanged, CP/M and floppy-based computer could be pur- time operating systems have minimal related programming tools chased for about one quarter of a pro- "interrupt windows" in which exter- olved into a family of portable op- grammer's annual salary. Quite nal interrupts are disabled. Real-time ages, and ap- simply, it was no longer necessary to operating systems such as the Intel share computer resources. RMX and National Starplex packages omputer resources Since that time, microprocessors provide this level of support. d dramatically with the in- have been applied to a variety of The emerging interest in local net- of microprocessors. Three works poses a new challenge to de- ts have precipitated a rev- signers of operating systems. Recent- on in computing: hand-threaded ly, Intel, DEC (Digital Equipment memory has been replaced by The 1 version of Corporation), and Xerox formed an ced semiconductor mem- CP/M ISbasically the alliance to promote Ethernet, a pack- ory; microprocessors have become same as the &bit ver- et-switchingnetwork intended topro- plentiful; and IBM decided that the vide point-to-point data transfer in an punched card is obsolete. Low-cost sionf the addition office environment. (In a packet- memory and processors have reduced of memow manage- switching network, data from several the cost of computer systems to a few ment and enhance- slow-speed sources, such as user ter- hundred dollars, but IBM's speci- merits to the file minals, is collected over local lines by fication of the floppy disk standard a single network node, which then has made the small computer system system. periodically transmits the data to its yseful. destination at a much higher speed, in ., In the early days of the 8080 micro- groups called packets.) In terms of ' -' Fj ,,$ processor, a small company called computing needs beyond replacement evolution and potential, Ethernet is j-cltbb:- Shugart Associates was taking shape of low-end minicomputers. Due to today what floppy disks were a:-+ , up the street from Intel. Shugart As- applications such as machine-tool decade ago. This inexpensive officej;i t{i; sociates, along with a number of movement and sensing, data acquisi- network performs such tasks as thewTfi r-2 other companies, viewed the floppy tion, and communications, current transfer of a form letter from data f--I disk as more than a punched card re- interest lies in real-time control. In a storage at one location to a rnernory;~ii~~ placement: at that time the primary real-time operating system, process typewriter in another part of the &' -% ...... ..... ... .logic -.-- '1 &d:':'ie*iepr:@-;r!I. .,- fhe-I&i&tion, dectranics accu&(e: -.g&r&t&h-' &i&@,&; . :: ' ., I :.. .: &&$@.'.&d,. .......................... fihaf&,-.tgh&h$E'e.~n-': ,:' .:. yndust+jj'.' :iypifj=i:(refilz+ent ufi$&std&,&≤' anh.,.-kffecfi$&a&'' @I 8640 miccqpr~<e~~?~?.:.;..... :.:. I ...... ;: - - .....thr6gg$.,.-k._n~i@eermgi .:. ~iginnitzi. .... ..': ptic.~&ok:progrhr%s .: ri!?: .;if0-.this -:' , . 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MASTER CARD. CASH. CHECK OR MONEY ORDER CALIFORNIA RESIDENTS ADD 6% SALES TAX - 8 June 1981 (n BBYIE Publicction~Inc Clroie 194 on inquiry card. building. When modifications are operating systems, but the most ex- facilities, but it excludes scientific fea- completed, the letter is typed locally citing new operating system techno- tures such as a complete transcen- or sent to a laser (or other) printer logy will develop around emerging dental-function library. that is a shared network resource. network hardware. In contrast to system languages Most timesharing systems handle a that run on a given machine, these network through simple file transfers Application Languages application languages would ideally between the machines (nodes) in the Application languages form the top contain no machinedependent fea- net, but real refinements occur when level of support for application pro- tures. An application language is the operating system itself is distrib- gramming. How does this level of either poorly designed or ill-suited for uted among the nodes. File access is language differ from other language a particular problem if the program- provided by one server node, while a levels? First and foremost, an applica- mer is forced to use extra-lingual con- computing function is performed by tion language contains the operations structs to access lower-level functions another. To the user, a requester and data types suitable for expressing of the operating system or machine. node appears as a powerful comput- programs in a particular problem en- The language must be a standard, ing facility, even though it may con- vironment. FORTRAN (FORmula without the necessity for various sist of only a local microprocessor, TRANslation), for example, was de- locally defined language extensions. a console, and a limited amount of signed in the late 1950s for scientific An extended standard language is of memory. applications; FORTRAN programs, limited value since the extensions are What refinements have been made therefore, consist primarily of alge- unlikely to exist in other implementa- to operating systems? Our models braic expressions operating upon tions. have been simplified; we understand binary floating-point numbers ex- The evolution of PL/I (Program- primitive operations required for pressed in scientific notation. How- ming Language/One) provides a reliable process synchronization in ever, FORTRAN contains only primi- good example of refinement in ap- real-time systems, and the human- tive file-access facilities and no plication languages. PL/I is not a new oriented interface in interactive decimal arithmetic, making it unsuit- invention: rather, it was defined by a subsystems has been improved. We able for commercial data processing. committee of IBM users in 1960 as a will, no doubt, continue to refine our COBOL (Common Business Ori- combination of ALGOL (ALGO- models for timesharing and real-time ented Language) has the commercial rifhmic Language), FORTRAN, and COBOL, with a liberal sprinkling of new facilities. ALGOL's principal contribution was block structure and nested constructs, while FORTRAN BUS-TO-BUS COMMUNICATION contributed scientific processing and COBOL added commercial facilities.