1. OPERATING SYSTEM OVERVIEW

2. Contents Basic hardware elements

3.   Most I/O devices are much slower than the processor Interrupts   Interrupt request signal   Active waiting cycle (polling)

4.   An interrupt cycle is added to the instruction cycle (fecth and execute).   The processor checks to see if an interrupt has occured (interrupt signal) Interrupt mechanism

5.   interrupt handler   interrupt vector Interrupt mechanism

6.   CPU saves PS and PC (push) into the control stack   CPU loads into PC and PS the corresponding values from the interrupt vector Interrupt processing

7.   iret   interrupt handler execution Interrupt processing

8. Interrupt enable/disable bit (PS register)   Hardware priority   STI (Set Interrupt) CLI (Clear Interrupt) Interrupt mechanism

9. main memory i+1 PS inth 1OO i i 149 15O iret 1OOO 12OO 12O1 main memory inthinth progprog interruptinterrupt 1 1 2 2 3 3 interrupt vector Interrupt processing

10. PS prog 12O1 3824 PS PC SP stack main memory 3824 39OO CPU completes execution of the current instruction Interrupt processing

11. interrupt signal has been accepted PS inth 1OO 3822 PS PC SP stack main memory 3824 39OO 12O1 PS prog 3823 3822 Interrupt processing

12. PS inth 151 3822 PS PC SP stack main memory 3824 39OO 12O1 PS prog 3823 3822 iret execution Interrupt processing

13. stack main memory 3824 39OO PS prog 12O1 3824 PS PC SP iret completed Interrupt processing

14. O.S.Components Contents

15.   Process Management O.S. COMPONENTS   Main-Memory Management   Secondary-Memory Management

16.   File Management   I/O-System Management O.S. COMPONENTS

17.   Creating and deleting processes   Suspending and resuming processes   Provide mechanisms for process interaction Process management

18. Keeping track of which parts of memory are currently being used and by whom Main memory management

19. Deciding which processes are to be loaded when memory becomes available Main memory management

20. Allocating and deallocating memory space as needed Main memory management

21. Secondary memory management   Free space management   Storage allocation   Disk scheduling

22. I/O SYSTEM MANAGEMENT The I/O subsystem consists of   A memory-management component that includes buffering and spooling

23.   A general device driver interface   Drivers for specific hardware devices   A general device driver interface   Drivers for specific hardware devices I/O SYSTEM MANAGEMENT The I/O subsystem consists of I/O SYSTEM MANAGEMENT The I/O subsystem consists of

24. File management   Creating and deleting files and directories   Supporting primitives for manipulating file and directory

25.   Mapping files onto storage   Backing up files on stable storage media File management

26. Protection systems   Mechanism for controlling the access of processes to system resources

27.   The mechanism must provide means for specifying the controls to be imposed and means for enforcement Protection systems

28.   The interface between users and O.S.   A program that reads and interpretes control statements   The interface between users and O.S.   A program that reads and interpretes control statements Comand-Interpreter System

29.   Its main function: to get next command statement and execute it (shell) Comand-Interpreter System

30. System calls Contents

31. Processes communicate with the O.S. and request services to it by making system calls System Calls

32. System calls provide the interface between any process and O.S. System Calls

33.   Process control Examples of System Call   Communications   Information management   Device manipulation   File manipulation

34. Corresponding to each system call there is a library procedure Corresponding to each system call there is a library procedure

35. count= read (file, buffer, nbytes) count returns the number of bytes actually read C program Example: read system call

36. Library read procedure operating system system call READ INT return from INT register x x  call parameters load x system call READ 2 3 1

37.   Puts the parameters of the system call in machine registers The library procedure   The control is returned to the caller by returning the status code as a result   Issues a INT instruction to start the O.S.

38.   directly via registers   in a memory block whose address is passed as a parameter in a registry   into the stack (push, pop)   directly via registers   in a memory block whose address is passed as a parameter in a registry   into the stack (push, pop) Methods to pass parameters to operating system

39. hardware (CPU, memory, disks, terminals, …) UNIX O.S. (process management, memory management, file system, I/O,...) standard library (open, close, read, write,..) utility programs (shell, compiler, …) users user mode kernel mode user int. library interface system call interf.

40. Dual mode of operations user mode   Hardware control does not allow the execution of privileged instructions   Used for normal execution of user programs

41.  Used for the execution of O.S. functions as required by system calls supervisor mode (kernel mode)  All instructions can be executed Dual mode of operations