Operating System Structure Part-I.pdf
- 1. Amrita School of Engineering, Bangalore Ms. Harika Pudugosula Teaching Assistant Department of Electronics & Communication Engineering
- 2. • Operating System Services • User and Operating System Interface • System Calls • Types of System Calls • System Programs • Operating System Structure 2
- 3. Objectives • To describe the services an operating system provides to users, processes, and other systems • To discuss the various ways of structuring an operating system • To explain how operating systems are installed and customized and how they boot 3
- 4. Operating System Services • Operating systems provide an environment for execution of programs and services to programs and users • One set of operating-system services provides functions that are helpful to the user: – User interface - Almost all operating systems have a user interface (UI). • Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch interface – Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error) – I/O operations - A running program may require I/O, which may involve a file or an I/O device 4
- 5. 5 fig: A view of Operating System Services
- 6. Cont.. • One set of operating-system services provides functions that are helpful to the user (Cont.): – File-system manipulation - The file system is of particular interest. Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management. – Communications – Processes may exchange information, on the same computer or between computers over a network • Communications may be via shared memory or through message passing (packets moved by the OS) – Error detection – OS needs to be constantly aware of possible errors • May occur in the CPU and memory hardware, in I/O devices, in user program • For each type of error, OS should take the appropriate action to ensure correct and consistent computing • Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system 6
- 7. • Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing – Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them • Many types of resources - CPU cycles, main memory, file storage, I/O devices. – Accounting - To keep track of which users use how much and what kinds of computer resources – Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other • Protection involves ensuring that all access to system resources is controlled • Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts 7 Cont..
- 8. User Operating System Interface - CLI CLI or command interpreter allows direct command entry – Sometimes implemented in kernel, sometimes by systems program – Sometimes multiple command implemented – shells – The main function of the command interpreter is to get and execute the next user-specified command • Primarily fetches a command from user and executes it – Two approaches that OS executes a task • the command interpreter itself contains the code to execute the command • OS implements most commands through system programs – Example: a command to delete a file naming file.txt – Sometimes commands built-in, sometimes just names of programs • If the latter, adding new features doesn’t require shell modification 8
- 9. Bourne Shell Command Interpreter 9
- 10. User Operating System Interface - GUI • User-friendly desktop metaphor interface – Usually mouse, keyboard, and monitor – Icons represent files, programs, actions, etc – Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder) – Invented at Xerox PARC • Many systems now include both CLI and GUI interfaces – Microsoft Windows is GUI with CLI “command” shell – Apple Mac OS X is “Aqua” GUI interface with UNIX kernel underneath and shells available – Unix and Linux have CLI with optional GUI interfaces (CDE, KDE, GNOME) 10
- 11. Touchscreen Interfaces n Touchscreen devices require new interfaces l Mouse not possible or not desired l Actions and selection based on gestures l Virtual keyboard for text entry l Voice commands. 11
- 12. The Mac OS X GUI 12
- 13. System Calls • System calls provide an interface to the services made available by an operating system • Typically written in a high-level language (C or C++) • Application developers design programs according to an application programming interface (API). • The API specifies a set of functions that are available to an application programmer, including the parameters that are passed to each function and the return values the programmer can expect. • Mostly accessed by programs via a high-level Application Programming Interface (API) rather than direct system call use • Three most common APIs are – Windows API for Windows System – POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and – Java API for the Java virtual machine (JVM) • Each operating system has its own name for each system call 13
- 14. 14 Example: Copy contents of one file to another file
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- 19. 19 fig: Example of how system calls are used
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- 21. System Call Implementation • Typically, a number associated with each system call – System-call interface maintains a table indexed according to these numbers • The system call interface invokes the intended system call in OS kernel and returns status of the system call and any return values • The caller need know nothing about how the system call is implemented – Just needs to obey API and understand what OS will do as a result call – Most details of OS interface hidden from programmer by API • Managed by run-time support library (set of functions built into libraries included with compiler) 21
- 22. API – System Call – OS Relationship 22 fig: The handling of a user application invoking the open() system call
- 23. System Call Parameter Passing • Often, more information is required than simply identity of desired system call – Exact type and amount of information vary according to OS and call • Three general methods used to pass parameters to the OS – Simplest: pass the parameters in registers • In some cases, may be more parameters than registers – Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register • This approach taken by Linux and Solaris – Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system – Block and stack methods do not limit the number or length of parameters being passed 23
- 24. Parameter Passing via Table 24
- 25. Types of System Calls • Process control – create process, terminate process – end, abort – load, execute – get process attributes, set process attributes – wait for time – wait event, signal event – allocate and free memory – Dump memory if error – Debugger for determining bugs, single step execution – Locks for managing access to shared data between processes 25
- 26. Types of System Calls (Cont.) • File management – create file, delete file – open, close file – read, write, reposition – get and set file attributes • Device management – request device, release device – read, write, reposition – get device attributes, set device attributes – logically attach or detach devices 26
- 27. Types of System Calls (Cont.) • Information maintenance – get time or date, set time or date – get system data, set system data – get and set process, file, or device attributes • Communications – create, delete communication connection – send, receive messages if message passing model to host name or process name • From client to server – Shared-memory model create and gain access to memory regions – transfer status information – attach and detach remote devices 27
- 28. • Protection – Control access to resources – Get and set permissions – Allow and deny user access 28 Types of System Calls (Cont.)
- 29. Examples of Windows and Unix System Calls 29
- 30. Standard C Library Example • C program invoking printf() library call, which calls write() system call 30
- 31. Example: MS-DOS • Single-tasking • Shell invoked when system booted • Simple method to run program – No process created • Single memory space • Loads program into memory, overwriting all but the kernel • Program exit -> shell reloaded At system startup running a program 31
- 32. Example: FreeBSD • Unix variant • Multitasking • User login -> invoke user’s choice of shell • Shell executes fork() system call to create process – Executes exec() to load program into process – Shell waits for process to terminate or continues with user commands • Process exits with: – status code = 0 – no error – status code > 0 – error code 32
- 33. System Programs • System programs provide a convenient environment for program development and execution. They can be divided into: – File manipulation – Status information sometimes stored in a File modification – Programming language support – Program loading and execution – Communications – Background services – Application programs • Most users’ view of the operation system is defined by system programs, not the actual system calls 33
- 34. System Programs • Provide a convenient environment for program development and execution – Some of them are simply user interfaces to system calls; others are considerably more complex • File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories • Status information – Some ask the system for info - date, time, amount of available memory, disk space, number of users – Others provide detailed performance, logging, and debugging information – Typically, these programs format and print the output to the terminal or other output devices – Some systems implement a registry - used to store and retrieve configuration information 34
- 35. System Programs (Cont.) • File modification – Text editors to create and modify files – Special commands to search contents of files or perform transformations of the text • Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided • Program loading and execution- Absolute loaders, relocatable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language • Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems – Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another 35
- 36. System Programs (Cont.) • Background Services – Launch at boot time • Some for system startup, then terminate • Some from system boot to shutdown – Provide facilities like disk checking, process scheduling, error logging, printing – Run in user context not kernel context – Known as services, subsystems, daemons • Application programs – Don’t pertain to system – Run by users – Not typically considered part of OS – Launched by command line, mouse click, finger poke 36
- 37. 37 References 1. Silberscatnz and Galvin, “Operating System Concepts,” Ninth Edition, John Wiley and Sons, 2012.
- 38. 38 Thank you