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Chapter 1: Introducing
Operating Systems
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What Is an OperatingSystem?
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A computer system consists of software (programs andhardware (the physical machine and its electronic components!
"he operating system software is the chief piece of software#the portion of the computing system that manages all of thehardware and all of the other software!
"o $e speci%c# it controls e&ery %le# e&ery de&ice# e&ery sectionof main memory# and e&ery nanosecond of processing time!
It controls who can use the system and how!
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Operating SystemSoftware
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"he pyramid shown in igure 1!1 is an a$stract representation of anoperating system and demonstrates how its ma)or components wor*together!
At the $ase of the pyramid are the four essential managers of e&eryoperating system: the Memory Manager, theProcessor Manager#the Device Manager, and the File Manager.
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A network was not always an integral part of operating systems+early systems were self,contained with all networ* capa$ilityadded on top of e-isting operating systems! .ow most operatingsystems routinely incorporate a Network Manager.
/egardless of the si0e or con%guration of the system# each of the
su$system managers must perform the following tas*s:
onitor its resources continuously 3nforce the policies that determine who gets what# when# and howmuch Allocate the resource when appropriate
4eallocate the resource when appropriateApplied Operating System 5
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"he emory anager (the su$)ect of Chapters 26' is incharge of main memory# also *nown as /A# short for /andomAccess emory! "he emory anager chec*s the &alidity of
each re7uest for memory space and# if it is a legal re7uest# itallocates a portion of memory that isn8t already in use! In amultiuser en&ironment# the emory anager sets up a ta$leto *eep trac* of who is using which section of memory! inally#when the time comes to reclaim the memory# the emory
anager deallocates memory!
A primary responsi$ility of the emory anager is to protectthe space in main memory occupied $y the operating systemitself9it can8t allow any part of it to $e accidentally or
intentionally altered!
ain emoryanagement
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"he ;rocessor anager (the su$)ect of Chapters 56ecause it handles the processes8 transitions from
one state of e-ecution to another# it can $e compared to atrac controller!
Once the ;rocessor anager allocates the processor# it sets upthe necessary registers and ta$les and# when the )o$ is %nished
or the ma-imum amount of time has e-pired# it reclaims theprocessor!
;rocessor anagement
Applied Operating System 0E'B# Jinu-# =.IK
Supercomputers I/IK# Jinu-# =.ICOS
Wor*stations# ser&ers Jinu-# =.IK# Windows
.etwor*s Jinu-# .etWare# =.IK# Windows
;ersonal digitalassistants
>lac*>erry# Jinu-# ;alm OS# Windowso$ile
A brief list of platforms andsample operating systemslisted in alphabetical
order.
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"ypes of OperatingSystems
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Operating systems for computers large and small fall into %&e categoriesdistinguished $y response time and how data is entered into the system:$atch# interacti&e# real,time# hy$rid# and em$edded systems!
%atc& systems date from the earliest computers# when they relied onstac*s of punched cards or reels of magnetic tape for input! Lo$s wereentered $y assem$ling the cards into a dec* and running the entire dec* ofcards through a card reader as a group9a $atch!
'nteractive systemsgi&e a faster turnaround than $atch systems $ut are
slower thanthe real,time systems we tal* a$out ne-t! "hey were introduced to satisfythe demandsof users who needed fast turnaround when de$ugging their programs!
Realtime systems are used in time,critical en&ironments where relia$ilityis *ey anddata must $e processed within a strict time limit! "he time limit need not $e
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y*rid systems are a com$ination of $atch and interacti&e!"hey appear to $e interacti&e $ecause indi&idual users can
access the system and get fast responses# $ut such a systemactually accepts and runs $atch programs in the $ac*groundwhen the interacti&e load is light!
+m*edded systems are computers placed inside other
products to add features and capa$ilities! or e-ample# you %ndem$edded computers in household appliances# automo$iles#digital music players# ele&ators# and pacema*ers!
Applied Operating System 1rief Distory of OperatingSystem 4e&elopment
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"he e&olution of operating system software parallels the e&olution of thecomputerhardware it was designed to control! Dere8s a &ery $rief o&er&iew of thise&olution!
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"he %rst generation of computers (1B561B was a time of &acuum tu$etechnologyand computers the si0e of classrooms! 3ach computer was uni7ue instructure and
purpose! "here was little need for standard operating system software$ecause eachcomputer8s use was restricted to a few professionals wor*ing onmathematical# scienti%c# or military applications!
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Second,generation computers (1B61B
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"hird,generation computers date from the mid,1B
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4e&elopment in the 1Bs dramatically impro&ed thecostEperformance ratio of computer components! Dardwarewas more Ge-i$le# with logical functions $uilt on easily
replacea$le circuit $oards!
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"he o&erwhelming demand for Internet capa$ility in the mid,1BBs spar*ed the proliferation of networ*ing capa$ility! "he
World Wide We$# concei&ed in a paper $y "im >erners,Jeemade the Internet accessi$le $y computer users worldwide# not)ust the researchers who had come to depend on it for glo$alcommunications!
4///s
"he new century emphasi0ed the need for operating systemsto oHer impro&ed Ge-i$ility# relia$ility# and speed! "o meet theneed for computers that could accommodate multipleoperating systems running at the same time and sharingresources# the concept of &irtual machines was de&eloped and$ecame commercially &ia$le!
Distory
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5irtuali6ation is the creation of partitions on a single ser&er# witheach partition supporting a diHerent operating system! In other
words# it turns a single physical ser&er into multiple &irtual ser&ers#often with multiple operating systems!
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7&readsulti,core technology helps the operating system handle threads#
multiple actions thatcan $e e-ecuted at the same time!
#*8ect#riented DesignAn important area of research that resulted in su$stantial eciencieswas that of the
system architecture of operating systems9the way their componentsare programmedand organi0ed# speci%cally the use of o*8ectoriented design and t&ereorgani6ation o"the operating system8s nucleus# the *ernel!
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9ey 7erms
*atc& system: a type of system de&eloped for the earliest computers that
used punched cards or tape for input# which were entered in a $atch!
central processing unit (P!): the component with the circuitry# theMchips#N tocontrol the interpretation and e-ecution of instructions!
core: the processing part of a C;= chip made up of the control unit and the
arithmeticlogic unit (AJ=!
Device Manager: the section of the operating system responsi$le forcontrolling theuse of de&ices! It monitors e&ery de&ice# channel# and control unit and chooses
the most ecient way to allocate all of the system8s de&ices!
em*edded system: a dedicated computer system# often small and fast# thatresides in alarger physical system such as )et aircraft or ships!
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main"rame: the historical name gi&en to a large computer systemcharacteri0ed $y itslarge si0e# high cost# and high performance!
Memory Manager: the section of the operating system responsi$le forcontrolling theuse of memory! It chec*s the &alidity of each re7uest for memory space and# ifit8s alegal re7uest# allocates the amount needed to e-ecute the )o$!
microcomputer: a small computer e7uipped with all the hardware andsoftwarenecessary to perform one or more tas*s!
minicomputer: a small to medium,si0ed computer system# also called amidrangecomputer!
multiprocessing: when two or more C;=s share the same main memory#most IEOde&ices# and the same control program routines! "hey ser&ice the same )o$stream ande-ecute distinct processing programs concurrently!
multiprogramming: a techni7ue that allows a single processor to processApplied Operating System 25
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network: a system of interconnected computer systems and peripheral de&icesthate-change information with one another!
Network Manager: the section of the operating system responsi$le forcontrollingaccess to and the use of networ*ed resources!
o*8ectoriented: a programming philosophy where$y programs consist ofselfcontained#reusa$le modules called o$)ects# each of which supports a speci%c function#$ut which are categori0ed into classes of o$)ects that share the same function!
operating system: the software that manages all the resources of a computersystem!
Processor Manager: a composite of two su$managers# the Lo$ Scheduler andthe;rocess Scheduler# which decides how to allocate the C;=!
realtime system: a computing system used in time,critical en&ironments thatre7uireguaranteed response times# such as na&igation systems# rapid transit systems#
andindustrial control s stems!
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so"tware: a collection of programs used to perform certain tas*s! Software fallsintothree main categories: operating system programs# compilers and assem$lers#and
application programs!
storage: a place where data is stored in the computer system! ;rimary storage ismainmemory and secondary storage is non&olatile media!
supercomputer: the fastest# most sophisticated computers made# used for
comple-calculations!
t&read: a portion of a program that can run independently of other portions!ultithreaded application programs can ha&e se&eral threads running at one timewith
the same or diHerent priorities!
t&roug&put: a composite measure of a system8s eciency that counts thenum$er of
)o$s ser&ed in a gi&en unit of time!
virtuali6ation: the creation of a &irtual &ersion of hardware or software!
Operating system&irtuali0ation allows a single C;= to run multiple operating system images at the
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