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Understanding Operating Systems Sixth Edition

Understanding Operating Systems Sixth Edition. Chapter 13 UNIX Operating System. Learning Objectives. After completing this chapter, you should be able to describe: The goals of UNIX designers The significance of using files to manipulate devices

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Understanding Operating Systems Sixth Edition

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  1. Understanding Operating SystemsSixth Edition Chapter 13 UNIX Operating System

  2. Learning Objectives After completing this chapter, you should be able to describe: • The goals of UNIX designers • The significance of using files to manipulate devices • The strengths and weaknesses of having competing versions of UNIX • The advantages of command-driven user interfaces • The roles of the Memory, Processor, Device, and File Managers in UNIX Understanding Operating Systems, Sixth Edition

  3. Overview • Three major advantages of UNIX • Portability • Code written in high-level language (C language) • Powerful utilities • Brief, single operation commands • Combinable into single command • Application device independence • Configurable to operate on any device type • Disadvantages • No single standardized version • Brief, cryptic commands difficult for novice learner Understanding Operating Systems, Sixth Edition

  4. History • Research project originally in 1965 • Joint venture between Bell Labs, AT&T, General Electric, and MIT • Goal • Develop MULTICS • MULTICS ambition • Serve diverse user group needs • Too intricate, complex, large for commercial value • Bell labs withdrew in 1969 Understanding Operating Systems, Sixth Edition

  5. History (cont'd.) Understanding Operating Systems, Sixth Edition

  6. History (cont'd.) Understanding Operating Systems, Sixth Edition

  7. The Evolution of UNIX • Original language • DEC PDP-7 assembly language • First official version: 1971 • Design • Do one thing well • Ran on DEC PDP-11 • No pipes or filters • Added in version 2 • Thompson and Ritchie: version 3 • New programming language (C language) Understanding Operating Systems, Sixth Edition

  8. The Evolution of UNIX (cont'd.) • AT&T forbidden to sell software • Universities and developers advanced software • Commercial transformation • Berkley BSD version: 1973-1975 • 1984: government deregulation • AT&T personal computer with UNIX System 4 • Contained additional Berkley version features • AT&T System 4 promotion as standard fails • 1990: two dozen versions Understanding Operating Systems, Sixth Edition

  9. The Evolution of UNIX (cont'd.) • 1991: AT&T UNIX system laboratories • Develops System V release 4 • Features • System V release 3, BSD 4.3, SunOS, Xenix • “The Open Group” formed • Owns UNIX trademark • 1993: Berkeley • 4.4 BSD: based on AT&T’s UNIX (AT&T license) • Novell acquires UNIX from AT&T Understanding Operating Systems, Sixth Edition

  10. The Evolution of UNIX (cont'd.) • Current releases • Modify “do one thing well” position • Commands more difficult to use • Pipelines preserved • Adaptable to new situations with ease • Meet new user needs • Full local area network support • Comply with international standards • Security improved • Uses Common Desktop Environment (CDE) • ISO/IEC 9945:2003 Standard Understanding Operating Systems, Sixth Edition

  11. Design Goals • Thompson and Ritchie vision • UNIX operating system • Created by programmers for programmers • Fast, flexible, easy-to-use • Immediate goals • Support software development • Included utilities for customized code • Utilities designed for simplicity: do one thing well • Small manageable sections of code • Keep algorithms simple • Based on simplicity, not sophistication Understanding Operating Systems, Sixth Edition

  12. Design Goals (cont'd.) • Long-term goal • Portability • Reduces conversion costs • Application packages not obsolete • Achieved with UNIX version 4 • Hardware independent • POSIX • Portable operating system interface for computer environments • IEEE standards defining portable operating system interface • IEEE STD. 1003.1 (2004 edition) Understanding Operating Systems, Sixth Edition

  13. Memory Management • Multiprogramming systems • Swapping (small jobs) • Entire program in main memory before execution • Program size restriction • Round robin policy • Demand paging (large jobs) • More complicated hardware • Increases system overhead • Thrashing (under heavy loads) • Advantage: implements virtual memory concept Understanding Operating Systems, Sixth Edition

  14. Memory Management (cont'd.) • Typical internal memory layout (single user) • Program code • Data segment • Stack Understanding Operating Systems, Sixth Edition

  15. Memory Management (cont'd.) • Program code • Sharable portion of program • Reentrant code • Physically shared by several processes • Code protected: instructions not modified during normal execution • Data references: without absolute physical address • Space allocation • Program cannot release until all processes completed • Text table: tracks processes using program code Understanding Operating Systems, Sixth Edition

  16. Memory Management (cont'd.) • Data segment • After program code • Grows towardhigher memory locations • Nonsharable section of memory • Stack • Starts athighest memory address • Grows downward • Subroutine calls and interruptsadd information • Main memory • Process informationsaved when process interrupted • Nonsharable section ofmemory Understanding Operating Systems, Sixth Edition 16

  17. Memory Management (cont'd.) • UNIX kernel • Implements “system calls” • Memory boundaries for process coexistence • System calls • File Manager interaction and request of I/O services • Implements most primitive system functions • Permanently resides in memory • Uses LRU page replacement algorithm • Network PCs, single-user, and multi-user systems • Use same memory management concepts Understanding Operating Systems, Sixth Edition

  18. Process Management • Handles • CPU allocation • Process scheduling • Satisfaction of process requests • Kernel maintains tables • Coordinates process execution • Device allocation • Uses predefined policies • Select process from READY queue • Begin execution • Give time slice Understanding Operating Systems, Sixth Edition

  19. Process Management (cont'd.) • Process scheduling algorithm • Selects highest priority process to runfirst • Priority value: accumulated CPU time • Processes with large CPU time get lower priority • Compute-to-total-time ratio • System updates for each job everysecond • Total time process in system divided by used process CPU time • Ratio = one • CPU-bound job Understanding Operating Systems, Sixth Edition

  20. Process Management (cont'd.) • Process scheduling algorithm (cont'd.) • Processes with same computed priority • Handled by round robin • Interactive processes: low ratio (no special policies) • Balance I/O-bound jobs with CPU-bound jobs • Keeps processor busy • Minimizes waiting processes overhead Understanding Operating Systems, Sixth Edition

  21. Process Management (cont'd.) • Process scheduling algorithm (cont'd.) • Loading process from READY queue • Process with longest secondary storage time • Swap out process • Process waiting longest (disk I/O, idle) • When processor becomesavailable • Process selected may not be ready (waiting on I/O) • Determineinactive but ready for execution • Process priorities recalculated • Handled dynamically Understanding Operating Systems, Sixth Edition

  22. Process Table Versus User Table • Simple processes (nonsharable code) • Tables • Keep system running smoothly • Process table • Always resides in memory • Maintains text table • User table • Resides in memory while process is active • User table, process data segment, code segment • Swapped as needed Understanding Operating Systems, Sixth Edition

  23. Process Table Versus User Table (cont'd.) • Process table • Each entry contains: • Process identificationnumber • User identification number • Process memory address or secondary storageaddress • Process size and scheduling information • Set up when process is created • Deleted when process terminates Understanding Operating Systems, Sixth Edition

  24. Process Table Versus User Table (cont'd.) • Text table • Sharable code processes • Process table maintains • Contains: • Memory address or secondarystorage address of text segment (sharable code) • Count: tracks number of processes using code • Increased by one when process starts using code • Decreased by one when process stops using code • Count = 0: implies code no longer needed Understanding Operating Systems, Sixth Edition

  25. Process Table Versus User Table (cont'd.) • User table • Allocated to each active process • Stored in transient memory area • Contains: • User and group identification numbers • Determine file access privileges • Pointers to system’s file table • Every file process uses • Pointer to current directory • List of responses for various interrupts • All information accessible when process running Understanding Operating Systems, Sixth Edition

  26. Synchronization • UNIX • True multitasking operating system • Requires processes wait for certain events • Each event represented by integers • Equal to address oftable associated with event • Race occurs • Event happens during process transition decision • Wait for event and entering WAIT state Understanding Operating Systems, Sixth Edition

  27. Synchronization (cont'd.) • fork • Execute oneprogram from another program • Secondprogram • Given all first program attributes (open files) • Savefirst program in original form • Split program: two copies • Both run from statement after fork command • fork executed • “Process id” (pid) generated • Ensure each process has unique ID number Understanding Operating Systems, Sixth Edition

  28. Synchronization (cont'd.) Understanding Operating Systems, Sixth Edition

  29. Synchronization (cont'd.) • wait • Synchronize process execution • Suspend parent until child finished • Program IF-THEN-ELSE structure • Controlled by pid value • pid > zero: parent process • pid = zero: child process • pid < zero: error in fork call Understanding Operating Systems, Sixth Edition

  30. Synchronization (cont'd.) Understanding Operating Systems, Sixth Edition

  31. Synchronization (cont'd.) • exec • Start new program execution from another program • execl, execv, execls, execlp, and execvp • Successful exec call • Overlay second program over first • Only second program in memory • No return from successful exec call • Parent-child concept: does not hold • Each exec call • Followed by test ensuring successful completion Understanding Operating Systems, Sixth Edition

  32. Synchronization (cont'd.) Understanding Operating Systems, Sixth Edition

  33. Device Management • Device independence to applications • I/O device treated as special file type • Device files given name • Descriptors called “iodes” • Identifies devices, contains device information, stored in device directory • Device drivers • Subroutines working with operating system • Supervise data transmission • Between main memory and peripheral unit • Most common drivers included in UNIX Understanding Operating Systems, Sixth Edition

  34. Device Management (cont'd.) • Device driver kernel incorporation • During systemconfiguration • Recent UNIX versions • Program called config • Automatically creates conf.c • For any hardware configuration • conf.c contains parameters controlling resources • Number of internal kernel buffers and swap space size • conf.c contains twotables • bdevsw (“block I/O switch”) • cdevsw (“character I/O switch”) Understanding Operating Systems, Sixth Edition

  35. Device Classifications • Divide I/O system • “Block I/O” system (“structured I/O” system) • “Character I/O” system (“unstructured I/O” system) • Physical device identification • Minor device number • Major device number • Class: block or character Understanding Operating Systems, Sixth Edition

  36. Device Classifications (cont'd.) Understanding Operating Systems, Sixth Edition

  37. Device Classifications (cont'd.) • Class: block or character • Each has configuration table • Array of entry points intodevice drivers • Major device number • Index to array to access appropriate code (specific driver) • Minor device number • Passed as an argument to device driver • Access one of several identical physical devices • Block I/O system • Devices addressed as 512-byte block sequences • Allows device manager to buffer (reduce I/O traffic) Understanding Operating Systems, Sixth Edition

  38. Device Classifications (cont'd.) • Character class devices • Device drivers handle implementing characterlists • Example: terminal • Typical character device • Two input queues and one outputqueue • I/O procedure synchronized through hardware completion interrupts • Some devices belong to both classes • Examples: disk drives, tape drives Understanding Operating Systems, Sixth Edition

  39. Device Drivers • Special section in kernel • Includes instructions • Allows operating system communication with device • Disk drive’s device drivers • Use seek strategy tominimize arm movement • Kept in set of files • Loaded as needed • Case of seldomused devices • Kept in memory all the time • Loaded at boot time • Kept in /dev directory by default and convention Understanding Operating Systems, Sixth Edition

  40. File Management • Three file types • Directories • Ordinary files • Special files • Each enjoys certain privileges • Directories • Maintain hierarchical structure of file system • Users allowed to read information in directory files • Only system allowed directory file modification Understanding Operating Systems, Sixth Edition

  41. File Management (cont'd.) • Ordinary files • Users store information • Protection based onuser requests • Related to read, write, execute, delete functions performed on file • Special files • Device drivers providing I/O hardware interface • Appear as entries in directories • Part of file system (most in /dev directory) • Special filename indicates type of deviceassociation Understanding Operating Systems, Sixth Edition

  42. File Management (cont'd.) • Files stored as sequences of bytes • No structure imposed • Text files • Character strings • Linesdelimited by line feed, new line, character • Binary files • Sequences of binarydigits • Grouped into words as they appear in memory during program execution • Structure of files • Controlled by programs using them: not by system Understanding Operating Systems, Sixth Edition

  43. File Management (cont'd.) • Organizes disk into blocks of 512 bytes each • Divides disk into four basic regions • First region (address 0): reservedfor booting • Second region: contains disk size and other regions’ boundaries • Third region includes: file definitions called “i-list” • Remaining region: free blocks availablefor file storage • Files stored in contiguous empty blocks • Simple allocation and no need to compact Understanding Operating Systems, Sixth Edition

  44. File Management (cont'd.) • “i-node” • Each entry in i-list called an “i-node” (or inode) • Contains 13 disk addresses • Contains specific file information • Owner’s identification • Protection bits, physical address, file size • Time of creation, last use, and last update • Number of links • File type • Directory, ordinary file, or special file Understanding Operating Systems, Sixth Edition

  45. File Naming Conventions • Case-sensitive filenames • 255 character length • No file naming conventions • Some compilers expect specific suffixes • Supports hierarchical tree file structure • Root directory identified by slash (/) Understanding Operating Systems, Sixth Edition

  46. File Naming Conventions (cont'd.) Understanding Operating Systems, Sixth Edition

  47. File Naming Conventions (cont'd.) • Path name rules • Path name starting with slash • Root directory • Path name • One name or list of names: separated by slashes • Last name on list: filename requested • Two periods (..) in path name • Moves upward in hierarchy(closer to root) • Only way to go up hierarchy • All other pathnames go down tree • Spaces not allowed within path names Understanding Operating Systems, Sixth Edition

  48. Directory Listings • “long listing” • Eight pieces of informationfor each file • First column • Shows file type and access privileges for each file • Firstcharacter: nature of file or directory • Next three characters: access privileges granted file owner • Next three characters: access privileges granted otheruser’s group members • Last three characters: access privileges grantedto users at large (system-wide) Understanding Operating Systems, Sixth Edition

  49. Directory Listings (cont'd.) • Second column • Indicates number of links (number of aliases) • Referring to same physical file • Aliases • ImportantUNIX feature: support file sharing • Several users work together on same project • Shared files appear in different directoriesbelonging to different users • Filename: may be different fromdirectory to directory • Eventually number will indicate when file no longer needed: canbe deleted Understanding Operating Systems, Sixth Edition

  50. Directory Listings (cont'd.) Understanding Operating Systems, Sixth Edition

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