Operating Systems History Pre 1950 the very first

Operating Systems: History • Pre 1950 : the very first electronic computers – valves and relays – no OS – single program with dedicated function • Pre 1960 : stored program valve machines – single job at a time – OS just consists of a program loader program CPU printer 1

Operating Systems: History • 1960: transistor machines – example: DEC PDP-8 » first Edinburgh Univ. computer, 1965 » 4 K 12 bit words of magnetic core memory; 1. 5 sec cycle time – RIM loader read in Binary loader – Binary loader read in executable from paper tape » a primitive BIOS – user program drives I/O devices directly » usually by polling » interrupts also possible – ‘walk up and use’ computer – illustrates ‘data rate mismatch’ problem 2

Operating Systems: History • Post 1960 : Batch systems on mainframe computers – collections of jobs made up into a batch – example: IBM 1401/7094 » card decks spooled onto magnetic tape and from tape to printer – example: English Electric Leo KDF 9 » first Edinburgh Univ. mainframe, 1968 » 32 K 48 bit words, 2 sec cycle time » punched paper tape input ‘walk up’ service or spooling via mag tape 3

Operating Systems: History • OS consisted of an input/output system for reading and writing magnetic tapes and a command interpreter for JCL on cards – speed mismatch problem reduced with fast mag tape but not removed – pipelining allowed next job to be read in whilst results of previous job being written to mag tape 4

Operating Systems: History • 1965: Multiple Job Stream Batch Systems – several jobs resident in memory together OS job 1 job 2 job 3 – a multiprogramming OS » CPU switched around the jobs in turn » I/O delays overlapped with other running jobs » jobs stay resident until finished 5

Operating Systems: History • IBM MFT - ‘Multiprogramming with Fixed Tasks’ – fixed partition boundaries • IBM MVT - ‘Multiprogramming with Variable Tasks’ – dynamic partition sizes and positions – OS scheduled jobs to minimise memory wastage 6

Operating Systems: History – example: Manchester University ATLAS, 1963 » 32 kwords 48 bit memory 1 sec cycle time » multiprogramming batch system » used remotely by Edinburgh Univ. via off line paper tape • Problems introduced by multiprogramming: – jobs had to run at different places in memory – inefficient use of expensive memory – one job could interfere with another e. g. overwrite other jobs memory – jobs could clash over use of I/O devices 7

Operating Systems: History • Overcome by using: – relocating linkers and loaders – hardware relocation base and limit registers » read/write/execute protected access – OS controlled access to I/O devices • Virtual memory architectures » pages and demand-paging » invented in Manchester and used first on ATLAS » 512 word pages + swap disc » segmentation came later 8

Operating Systems: History • 1970: Multi-Access Interactive Time-Sharing Systems – powerful machines very expensive – need to share use between many users – simultaneous interactive use – new OS and software technology for time-sharing » virtual memory pages and segments » processes with a continuing existence, not just for life of job execution memory resident, swapped out to disc, blocked, waiting etc. » command interpreters, on line editors » file systems, back up and archiving » TTY terminals no VDUs until later » still stand alone no networking 9

Operating Systems: History Various Development Projects • Project MAC at MIT on IBM 7094, 1966 • MULTICS by a consortium on GE 645, 1969 • EMAP in Edinburgh University on EEC 4 -75, 1970 – joint project with ICL – 4 -75: 1 Mb memory, 4 kb pages and 64 kb segments – 50 simultaneous users – used in Edinburgh until 1989 – ported onto ICL 2900 in mid-1970 s » 100 users » dual processor version – final port onto NEC (IBM 370 clone) » 100 s of users – overtaken by UNIX-based systems 10

Operating Systems: History • Mini-computer systems – DEC VAX (VMS Operating System), Prime, Wang, Interdata, . . . . – between mainframes and workstations in cost and performance • Workstation systems – increasingly cost-effective since 1980 – Sun, IBM PC, Apple Mac • Networks of workstations – ethernet, token rings etc. • Parallel systems – large numbers of loosely connected machines – only a minimal OS in each » usually a separate front end machine running a normal OS for I/O – examples: Connection Machine, Cray T 3 E in EPCC etc. 11