Operating System

1.  AT&T: AmericanTelephone andTelegramCompany
 A significantthingaboutBell labsis In Bell Labs50% of people are Producingsoftwaresand
other50% of themhave directinvolvementwithsoftwares
 The main problemintodays worldisthatwe needuseful softwaresof effective workingbut
we don’thave enoughpeople forwritingsoftwares.
 In mythical manmonthsfredbookestimatesthatittookabout500 staff yearsof effortsto
produce operatingsystemforIBMs360 seriescomputers
 Whenken Thompsonand denisritchi startedthe unix systemin1969 theyfounda structure
that simplifiesmanyaspectsof interactionsbetweencomputersandpeople
 Thomsomand ritchi were aimingtokeeptheirsystemsimpleandtheyfoundacollectionof
primitivesthatenable themtodoa great deal withthe veryfew primitives.
 A unix systemismade upof sort of three layers
 The central layerKERNEL controlsthe resourcesof the machine thenitis wrappedin
somethingcalledshell whichisthe interface betweenuserandkernel partitsitsthere and
waitsfor youto write commandsandtheninterpretthemandthenarounditthere is
utilitieslikeprograms
 What youcan dois to thinkof these unix systemprogramslike somebuildingblockswith
whichyoucan create things
 The thingwhichdistinguishUNIXfromothersystemsisthe degreetowhichthose building
blockscan gluedtogetherinmanydifferentwaystogetmanydifferentjobsdone .the
systemisveryflexible
 Example:
Spell checkingsoftware:
We can glue differentunix programstomake suchsoftware
 Breakthe sentence intowords
 Lowercase
 Arrange theminsortedorder
 Use functionUNIQUEto remove duplicate words
 Program mismatch
 A time shared operating systemallowsmultiple usersto share computers simultaneously.
Each action or order at a time the shared systembecomes smaller,so onlya little CPU
time is requiredfor each user. As the systemrapidlyswitchesfrom one user to another,
each user is giventhe impressionthat the entire computer system isdedicatedto its use,
although it isbeing sharedamong multiple users.

2.  Single-level storage (SLS) or single-level memory is a computer storage term which
has had two meanings. The two meanings are related in that in both, pages of memory
may be in primary storage (RAM) or in secondary storage (disk), and that the physical
location of a page is unimportant to a process.
 Multics ("Multiplexed Information and Computing Service") is an influential
early time-sharing operating system based on the concept of a single-level memory.[4][5]
It
has been said that Multics "has influenced all modern operating systems since, from
microcomputers to mainframes."[6]
 Initial planning and development for Multics started in 1964, in Cambridge,
Massachusetts. Originally it was a cooperative project led by MIT (Project
MAC with Fernando Corbató) along with General Electric and Bell Labs. It was
developed on the GE 645 computer, which was specially designed for it; the first one was
delivered to MIT in January, 1967.
 Multics(MultiplexedInformationandComputingService) wasa mainframe time-
sharingoperatingsystem thatwasdevelopedinthe 1963-1969 periodthroughthe
collaborationof the MassachusettsInstituteof Technology(MIT),GeneralElectric(GE),and
Bell Labs.Multicswas the firstor one of the firstoperatingsystemsthatusedpage-
segmentedstorage.The operatingsystemwaswrittenin PL/I andran on GE hardware.By
1970, Bell Labshad withdrawnfromthe project,andHoneywell,whichhadboughtGE's
computerdivision,continuedasthe hardware provider.Supportfromthe Advanced
ResearchProjectsAgencyhelpedsustainthe project.
