The document discusses operating system structure and system calls. It defines system calls as the programming interface to OS services, accessed via APIs. It provides examples of common system call types like process control, file management, and inter-process communication using pipes. It also contrasts examples of running programs on single-tasking MS-DOS versus multi-tasking Unix variants like FreeBSD which uses processes and forking.

1. DEPARTMENT OF COMPUTER SCIENCE & ENGINEERING
CSS308 – OPERATING SYSTEMS
IIIYEAR / V SEMESTER
Prepared by
Dr.Thanuja R
Assistant Professor/ CSE

2. UNIT-I
OPERATING SYSTEMS OVERVIEW
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE
Introduction: What Operating systems do - Structure -
Operations - Process management -Operating system Structure:
Services - User Interfaces - Systems calls and types – Systems
programs - Design and implementation - Operating System
Structure - System boot

3. SystemCalls
 Programminginterface to the servicesprovided by the O
S
 Typicallywritten in ahigh-levellanguage(Cor C++)
 Mostly accessed by programs via a high-level Application Programming
Interface(API)rather than direct systemcalluse
 Three most common APIs are Win32 API for Windows, POSIXAPI for
POSIX-basedsystems (including virtually all versions of UNIX, Linux, and
MacO
SX),andJavaAPIfor the Javavirtual machine (JVM)
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

4. Exampleof SystemCalls
 Systemcall sequenceto copythe contents of one file to another file
4

5. SystemCallImplementation
Typically,anumber associatedwith eachsystemcall
System-callinterfacemaintains atable indexedaccordingto these
numbers
The system call interface invokes the intended system call in OS
kernel and returns status of the systemcall and any return values
The caller need know nothing about how the system call is
implemented
Justneedsto obeyAPIandunderstand what OSwill do asaresult call
Most details of OSinterface hidden from programmer byAPI
Managedbyrun-time supportlibrary (set of functionsbuilt into libraries
included with compiler)
Why we use APIs rather than system call?
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

6. API–SystemCall–OSRelationship
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

7. SystemCallParameter Passing
Often, more information isrequired than simplyidentity of
desired systemcall
Exacttype andamount of information vary accordingtoOSand call
Threegeneral methods usedto passparameters to theOS
Simplest: passthe parameters inregisters
 In somecases,maybe more parameters thanregisters
Parametersstored in ablock, or table, inmemory, and addressof block
passedasaparameter in aregister
Thisapproach taken by LinuxandSolaris
Parametersplaced, or pushed,onto the stackby theprogram and
poppedoff the stackby the operatingsystem
Blockandstackmethods do not limit the number or length of
parameters beingpassed
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

8. Parameter Passingvia Table
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

9. Typesof SystemCalls

10. Typesof SystemCalls
Processcontrol
create process,terminateprocess
end, abort
load, execute
get processattributes, set processattributes
wait fortime
wait event, signalevent
allocate and free memory
Dump memory if error
Debuggerfor determining bugs,singlestep execution
Locksfor managingaccessto shareddata betweenprocesses
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

11. Typesof SystemCalls
 Filemanagement
 create file, deletefile
 open, closefile
 read, write, reposition
 get and set fileattributes
 Devicemanagement
 request device, releasedevice
 read, write, reposition
 Get& set deviceattributes
 logically attach or detachdevices
 Protection
 Control accessto resources
 Getand setpermissions
 Allow and denyuseraccess
 Information maintenance
 gettime or date,set time or date
 get systemdata, set systemdata
 get and set process,file, ordevice
attributes
 Communications
 create, delete communication
connection
 send,receive messagesif message
passingmodelto hostnameor
processname
Fromclientto server
 Shared-memorymodelcreate and
gainaccessto memoryregions
 transfer statusinformation
 attach and detach remotedevices

12. Pipe() system call Communications

13. PIPE() …
•int pipe(int fds[2]);
Parameters :
• fd[0] will be the fd(file descriptor) for the read
end of pipe.
•fd[1] will be the fd for the write end of pipe.
Returns : 0 on Success. -1 on error.

14. Ex:Windows and Unix SystemCalls
StandardCLibraryExample
 C program invoking
printf() library call,
which calls write()
system call
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

15. Example:MS-DOS
 Single-tasking
 Shellinvoked whensystem
booted
 Simplemethod torun
program
 Noprocesscreated
 Singlememory space
 Loadsprogram into memory,
overwriting all but thekernel
 Programexit ->shellreloaded
At system startup running a program
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

16. Example:FreeBSD
 Unix variant
 Multitasking
 Userlogin ->invokeuser’schoiceofshell
 Shellexecutesfork() systemcall tocreate
process
Executesexec()to load programinto
process
Shellwaits for processto terminateor
continues with usercommands
 Processexits with:
 code=0 –no error
 code>0 –error code
CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE

17. CSS308-OPERATING SYSTEMS / Dr.Thanuja R/ AP/ CSE