IT2164/IT2561 Operating Systems and Administration Chapter 1 Introduction to Operating Systems PDF

IT2164/IT2561 Operating Systems and Administration Chapter 1 Introduction to Operating Systems Introduction to Operating Systems At the end of this chapter, you should be able to Define what is an operating system Describe the difference between system software and application software...

IT2164/IT2561 Operating Systems and Administration Chapter 1 Introduction to Operating Systems Introduction to Operating Systems At the end of this chapter, you should be able to Define what is an operating system Describe the difference between system software and application software Describe concepts of resource abstraction and resource sharing Understand technique of multiprogramming Understand Operating System strategies Introduction to Operating Systems An operating system is a program that acts as an intermediary between the user of a computer and the computer hardware Provide an environment in which user can execute programs in a convenient and efficient manner Performs no useful function by itself Introduction to Operating Systems Why study Operating System ?  Understand the model of operation Easier to see how to use the system Enables you to write efficient code  Learn to design an OS Even so, OS is pure overhead of real work Application programs have the real value to person who buys the computer Computers and Software Computer systems consist of software and hardware Software is differentiated according to its purpose  Application software is software that allows the user to perform some intended task, function or activity and includes productivity tools.  System software provides an interface with hardware and serves as a platform for running programs and maintaining the efficiency of the system. It can be divided into operating systems and utility programs  Perspectives of the Computer print open() start-printer cut malloc() read-disk save send fork() track-mouse Application Application Application Software Software Software System System System Software Software Software Hardware Hardware Hardware (a) End User (b) Application (c) OS Programmer View Programmer View View System Software System software provides two kinds of environment  Allows human users to interact with the computer  Provides tools and subassemblies used with application programs Independent of individual applications, but common to all of them Examples  C library functions  A window system  A database management system  Resource management functions  The OS Using the System Software Application Programmer Software API Command Line Loader System Software Interpreter Window System Libraries Libraries Compiler Libraries Database OS Management System Hardware  Application Software, System Software, and the OS Human-Computer Interface Application Software API There is a hierarchy among application System Software software, system software (More Abstract Resources) and the OS. The OS uses the functionality at the OS Interface software-hardware interface to implement the Trusted OS OS interface. The system (Abstract Resources) software uses the OS interface to export the API. Application programs use Software-Hardware Interface the API to create software that implements the human-computer interface. Hardware Resources The OS as a Resource Manager Resource: Anything that is needed for a executing program to run  Memory  Space on a disk  The CPU Operating system can be viewed as a resource manager  “An OS creates resource abstractions”  “An OS manages resource sharing” Resource Abstraction Abstraction is when an OS hides the actual tasks needed to manage and use resources Allows user programs to use these resources by using simpler commands to access these resources. Makes it easy for user programs to use resources in a computer system. Resource Abstraction Examples:  Writinga file to disk  Displaying text/graphics on screen  Running an application Simplifies usage but limits flexibility  Certain operations become easy to perform while other operations may be impossible to achieve Resource Abstraction Example- Copying information from memory to disk load(block, length, device); seek(device, 236); out(device, 9) write(char *block, int len, int device, int track, int sector) {... load(block, length, device); seek(device, 236); out(device, 9);... } write(char *block, int len, int device,int addr); fprintf(fileID, “%d”, datum); Disk Abstractions Application Programmer OS Programmer int fprintf(…) {... void write() { write(…) load(…); … seek(…) } load(…); seek(…); out(…) out(…); } (a) Direct Control (b) write() (c) fprintf() abstraction abstraction Abstract Resources User Interface Application Abstract Resources (API) Middleware OS Resources (OS Interface) OS Hardware Resources Resource Sharing Two kinds of sharing  Space-multiplexed sharing The resource is divided into two or more distinct units and each unit is allocated to different processes  Time-multiplexed sharing The entire resource is allocated to a process for a period of time, after which it is then allocated to another process and so on. Resource Sharing Abstract Abstract Abstract Machine Pi Machine Pj Machine Pk … OS Resource Sharing Pi Memory Pk Memory … Time-multiplexed Physical Processor Pj Memory Space-multiplexed Physical Memory Multiprogramming Refers to the technique for sharing the CPU among runnable processes How does it work ?  Process may be blocked on I/O  Process may be blocked waiting for other resource, including the CPU  While one process is blocked, another might be able to run  Increases CPU utilization Multiprogramming OS accomplishes CPU sharing “automatically” – scheduling Speeding Up the Car Wash Vacuum Wash Dry Inside (a) The Sequential Car Wash Vacuum Inside Wash Dry (b) The Parallel Car Wash Speeding up the Car Wash Vacuum Inside T=1 Vacuum Inside Wash Dry T=1 Wash Dry Vacuum Vacuum Wash Dry T=2 Inside Inside Wash Dry T=2 Vacuum Wash Dry T=3 Vacuum Inside Inside Wash Dry T=3 Vacuum Inside Wash Dry T=4 Vacuum Inside T=4 Wash Dry Vacuum Inside Wash Dry T=5 Vacuum Inside Wash Dry T=5 (a) The Sequential Car Wash (b) The Parallel Car Wash Multiprogramming Performance Pi’s Total Execution Time, ti Time 0 ti (a) Pi’s Use of Machine Resources P1 P2 … Pi … PN Time (a) All Processes’ Use of Machine Resources Using the processor I/O operation OS Strategies Different strategies have been used to provide OS services Refers to the general characteristics of the programmer’s abstract machine. Depends on business and engineering criteria  How will the computer be used?  Is human interaction important?  Will there be more than one person using?  Is response time critical? OS Strategies Batch processing Timesharing Personal computer & workstations Others  Process control & real-time  Network  Distributed  Small computers Batch Processing Job 3 Job 19 Input Spooler Output Spooler Input Spool Output Spool Batch Processing Uses multiprogramming Job (file of OS commands) prepared offline Batch of jobs given to OS at one time OS processes jobs one-after-the-other No human-computer interaction OS optimizes resource utilization Batch processing (as an option) still used today A Shell Script Batch File cc -g -c menu.c cc -g -o driver driver.c menu.o driver < test_data > test_out lpr -PthePrinter test_out tar cvf driver_test.tar menu.c driver.c test_data test_out uuencode driver_test.tar driver_test.tar >driver_test.encode Timesharing Systems Abstract Machines Result Physical Command Machine Result Command … Result Command Timesharing Systems Uses multiprogramming Support interactive computing model (Illusion of multiple consoles) Different scheduling & memory allocation strategies than batch Tends to propagate processes Considerable attention to resource isolation (security & protection) Tend to optimize response time Examples of Modern OS UNIX  Developed by AT&T Bell labs researchers in 1970  Due to need for a simple, small OS  Primarily a command line oriented operating system  Open operating system – easier to extend  Variants: System V Unix, BSD Unix, HP-UX, Sun Solaris, Mach OS  Development of standardised UNIX system call interface – POSIX.1  Time sharing OS Examples of Modern OS Linux  “Open source UNIX”  Developed by Linus Torvalds for 80386 processor in 1991  Evolved as collaboration by many users corresponding over internet  Variants :Redhat Linux, SuSE Linux  Multiuser, multitasking OS with full set of UNIX- compatible tools  Recent work concentrates on standardization: POSIX Examples of Modern OS Windows family of OS  Evolves through Windows 3.x, Windows 95/98, Windows NT/ 2000/XP, Windows Vista, Windows CE, Windows Mobile  Heavily window-oriented  Command line available – cmd.exe  Object oriented design  Heavy use of threads  File system: FAT, FAT32, NTFS, DFS  Active Directory – authentication, rights, policies  System call interface – Win32 API The Microsoft OS Family Win32 API Win32 API Subset Win32 API SubSet Windows CE (Pocket PC) Windows 95/98/Me Windows NT/2000/XP/7 Conclusion Operating systems perform overhead, but critical tasks in the functioning of a computer system. Many different OSs are developed for different purposes. The modern OS uses resource abstractions and sharing to allow programs to use resources. Operating systems aims to maximize use of computer resources without the user’s or program’s involvement.