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Transcript
Chapter 2: System Structures Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013 Operating System Services n Operating systems provide an environment for execution of programs and services to programs and users n One set of operating-system services provides functions that are helpful to the user: l User interface - Almost all operating systems have a user interface (UI). 4 Varies between Command-Line (CLI), Graphics User Interface (GUI), Batch l 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) l I/O operations - A running program may require I/O, which may involve a file or an I/O device l 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. Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 Operating System Services (Cont.) l Communications – Processes may exchange information, on the same computer or between computers over a network 4 l 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 4 May occur in the CPU and memory hardware, in I/O devices, in user program 4 For each type of error, OS should take the appropriate action to ensure correct and consistent computing 4 Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 Operating System Services (Cont.) n Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing l Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them 4 Many types of resources - Some (such as CPU cycles, main memory, and file storage) may have special allocation code, others (such as I/O devices) may have general request and release code l Accounting - To keep track of which users use how much and what kinds of computer resources l 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 4 Protection involves ensuring that all access to system resources is controlled 4 Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts 4 If a system is to be protected and secure, precautions must be instituted throughout it. A chain is only as strong as its weakest link. Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 Types of System Calls n Process control l end, abort l load, execute l create process, terminate process l get process attributes, set process attributes l wait for time l wait event, signal event l allocate and free memory l Dump memory if error l Debugger for determining bugs, single step execution l Locks for managing access to shared data between processes Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 Types of System Calls n n File management l create file, delete file l open, close file l read, write, reposition l get and set file attributes Device management l request device, release device l read, write, reposition l get device attributes, set device attributes l logically attach or detach devices Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 Types of System Calls (Cont.) n n Information maintenance l get time or date, set time or date l get system data, set system data l get and set process, file, or device attributes Communications l create, delete communication connection l send, receive messages if message passing model to host name or process name 4 From client to server l Shared-memory model create and gain access to memory regions l transfer status information l attach and detach remote devices Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 Types of System Calls (Cont.) n Protection l Control access to resources l Get and set permissions l Allow and deny user access Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 System Programs n n System programs provide a convenient environment for program development and execution. They can be divided into: l File manipulation l Status information sometimes stored in a File modification l Programming language support l Program loading and execution l Communications l Background services l Application programs Most users’ view of the operation system is defined by system programs, not the actual system calls Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 System Programs n Provide a convenient environment for program development and execution l Some of them are simply user interfaces to system calls; others are considerably more complex n File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories n Status information l Some ask the system for info - date, time, amount of available memory, disk space, number of users l Others provide detailed performance, logging, and debugging information l Typically, these programs format and print the output to the terminal or other output devices l Some systems implement a registry - used to store and retrieve configuration information Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 System Programs (Cont.) n File modification l Text editors to create and modify files l Special commands to search contents of files or perform transformations of the text n Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided n Program loading and execution- Absolute loaders, relocatable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language n Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems l 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 Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 System Programs (Cont.) n Background Services l Launch at boot time 4 Some for system startup, then terminate 4 Some from system boot to shutdown l Provide facilities like disk checking, process scheduling, error logging, printing l Run in user context not kernel context l Known as services, subsystems, daemons n Application programs l Don’t pertain to system l Run by users l Not typically considered part of OS l Launched by command line, mouse click, finger poke Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013 System Boot n When power initialized on system, execution starts at a fixed memory location l n Firmware ROM used to hold initial boot code Operating system must be made available to hardware so hardware can start it l Small piece of code – bootstrap loader, stored in ROM or EEPROM locates the kernel, loads it into memory, and starts it l Sometimes two-step process where boot block at fixed location loaded by ROM code, which loads bootstrap loader from disk n Common bootstrap loader, GRUB, allows selection of kernel from multiple disks, versions, kernel options n Kernel loads and system is then running Operating System Concepts – 9th Edition 2.* Silberschatz, Galvin and Gagne ©2013