IT 3123 Hardware and Software Concepts

Transcription

2 Operating System and Application Application program: solves specific problems or performs specific functions Payroll Word processing Web server Operating system: supports the application by providing user interfaces, hardware interfaces, and resource management The hardware and the OS together define a virtual machine. 2

3 Bare Bones Computer System Does not load instructions into main memory No user interface except for I/O routines provided with executing program Is idle (or busy waiting) when waiting for user input No facility to store, retrieve, or manipulate files No ability to control peripheral devices Can run only one program at a time 3

4 Integrated Computer Environment Operating System 4

5 Operating System Basic Services Act as an interface between the user and the system Accept commands and requests from a user and a user s program (interface between application program and hardware.) Manage, load, and execute programs Manage hardware resources of the computer 5

6 Additional Services Provides a means of starting the computer Bootstrapping or booting the computer (also called Initial Program Load, or IPL) Provides file system services Handles all interrupt processing Provides I/O support services 6

7 Additional Services Provides interfaces for the user s programs Provides network services Provides tools and services for concurrent processing 7

8 Services Required for Concurrent Processing Allocates resources such as memory, CPU time, and I/O devices to programs Protects users and programs from each other (with help from the hardware) Provides for inter-program communication Provides feedback to the system administrators to permit performance optimization of the computer system 8

9 Memory-Resident OS Parts Memory Resident: always loaded in memory Commonly called the kernel Contains essential services required by other parts of the operating system and applications. Typically responsible for managing memory management, processes and tasks, and secondary storage 9

10 Non Memory-Resident Applications Infrequently used programs, software tools, and commands These are loaded by the kernel as needed 10

11 Thin Clients Diskless workstations or thin clients Programs, including the OS, are located on another computer on the network Programs run in the memory of the diskless workstation Program loading takes place over the network. 11

12 Operating System Services User Application Command Interface File Services Core Services Network Services I/O Services Computer Hardware Network Hardware 12

13 OS Degree of Activity Interactive Also known as conversational systems Batch processing User submits programs or jobs for processing Little to no user interaction Event driven Interrupts or service requests 13

14 Hardware and the OS A hardware platform may support a variety of operating systems An operating system may work on a variety of platforms 14

15 Hardware and the OS A standard operating system that works on different hardware platforms: Provides program and file portability Enables user efficiency through recognizable interface Is (mostly) implemented through a systems programming language like C or C++ as opposed to assembly language 15

16 Single Job Processing Only one program is loaded into memory and executed Example: MS-DOS Memory resident components Command interface shell I/O routines, including BIOS File management system User program in control 16

17 OS Regains Control When program is finished control is transferred back to the command interpreter If the user s program requests I/O The user wishes to stop the program execution via a keyboard interrupt System malfunctions 17

18 Disadvantages Lack of security Single Job Processing Programs can overwrite the resident OS Programs can write directly to I/O devices System provides minimum memory management and no scheduling CPU is often idle awaiting the completion of I/O operations 18

19 Concurrent Operations Multitasking (multiprogramming) vs. multiprocessing which implies multiple CPUs Concurrent processing vs. simultaneous processing 19

20 Achieving Multitasking While one program is waiting for I/O to take place, another program is using the CPU to execute instructions. Interrupts notify CPU and OS when I/O is complete. Time-slicing: The CPU may be switched rapidly back and forth between different programs (Clock interrupts) Dispatching is the process of selecting which program to run at any given instant 20

21 Sharing the CPU during I/O Breaks I/O represents a large percentage of a typical program s execution 21

22 Time-sharing the CPU Time slicing Timer interrupt Timer interrupt 22

23 Program Dispatching Running I/O Request CPU Available Time Expired Waiting Ready I/O Complete (This is a state transition diagram. ) 23

24 Logical Equivalence of Hardware and Software Specialized hardware can be built to perform any function that can be implemented in software Software can be written to perform any function that hardware can perform. But, there has to be some hardware to run the software. 24

25 What the OS Needs from the Hardware Privileged instructions Protected memory A timer (clock) that can generate interrupts. 25

26 Privileged Instructions Some instructions (like I/O) instructions are reserved for the operating system. A mode bit in the CPU s status word is set when the OS is in control Privileged instructions work when the mode bit is set and generate an illegal instruction interrupt when it is not. 26

27 Protected Memory If any program can write to any memory location, a malicious or defective user program can damage OS code or data. Two ways to protect memory: Memory keys. These are bits like a mode bit attached to blocks of memory Virtual address spaces 27

28 A Timer Generates Interrupts The OS gets control whenever an application program requests I/O services What if an application program never requests I/O services? Part of the hardware is a timer. It generates an interrupt at (short) intervals. The OS gets control to handle the interrupt. Can cut off a long-running program. 28

29 Multiprogramming Two or more application programs in memory. Consider one CPU and more than one program. This can be generalized to more than one CPU. Also called multitasking or concurrent operation. 29

30 Multiprogramming A program may be in one of three states: Running: The program s instructions are being executed by the CPU I/O Wait: The program has requested I/O services from the operating system, and the I/O has not completed Ready: The program is not waiting for anything, but some other program is using the CPU. 30

31 Program Dispatching The operating system keeps three queues: Running (one program per CPU) Ready Waiting 31

32 Program Dispatching Programs in the running state are moved to: Waiting if they request I/O Ready if their time slice expires Programs in the waiting queue are moved to the ready queue when I/O completes Programs in the ready queue are moved to running when a CPU is available. 32

33 Program Dispatching Running I/O Request CPU Available Time Expired Waiting Ready I/O Complete 33

34 Program Dispatching Running I/O Request CPU Available Time Expired Waiting Ready I/O Complete OS loads new program 34 Program ends

35 Priority Scheduling Programs can have priority attributes The same three queues (running, ready, waiting) are used Higher priority programs go to the front of the line. (Or there are several ready queues.) Problem: How to prevent a low-priority process from being starved of CPU time. (One way is to increase its priority if it has been waiting a long time.) 35

36 Context Switching Context switching: changing what program is running on a CPU Save state of running program (registers, program counter) Establish state of new program Load program counter with starting address. 36

37 I/O Bound and CPU Bound I/O bound: a program that requires mostly I/O resources; the other processes are not using all the CPU, so the limit on speed is I/O; generally waiting. Give I-O bound programs high priority for the CPU CPU bound: a program that requires a lot of CPU time and little I/O; generally ready or running. Give CPU-bound programs lower priority for the CPU. 37

38 Operating System Services Command processor File management system I/O control system Network management, communication support, and communication interfaces System Administration 38

39 Operating System Services Process control management and interprocess communication Memory management System protection management 39

40 File Management File a named logical unit of storage Basic file management system provides Directory structures for each I/O device Tools to copy and move files Information about each file in the system and the tools to access that information Security mechanisms to protects files and control access 40

41 Additional File Facilities Backup, emergency retrieval and recovery File compression Transparent network file access Auditing Journaling (keeping a separate record of updates) 41

42 I/O Services Startup configuration Device drivers that implement interrupts and provide other techniques for handling I/O Optimizes completion of I/O tasks Plug and play device recognition Hot swapping, hot plugging 42

43 Process Control A process is an executing program A thread is an individually executable part of a process Inter-process messaging services Example: a pipe in Unix or DOS that is a temporary software connection between two programs or commands 43

44 Memory Management Identifies programs loaded into memory Allocates space to programs Recovers space released by programs Explicit release End of program Prevents programs from reading and writing memory outside of their allocated space 44

45 Security Management Protect OS from users Protect users from other users Prevent unauthorized entry to system Prevent unauthorized system use by authorized users 45

46 Network Services Interface between communication software and OS I/O control system that provides network access Locate and connect to other computers Access files, I/O devices, and programs from remote systems Support distributed processing 46

47 System Administration System configuration and setting group configuration policies Adding and deleting users,modifying user privileges File system management, backups Network administration Software installations and upgrades OS installations, patches, and upgrades System tuning and optimization 47

48 Operating System Organization Monolithic Hierarchical, layered Microkernel 48

49 49 Monolithic Kernel

50 50 Hierarchical ( Target Model )

51 51 Microkernel

52 Bootstrapping Execution begins with bootstrap loader (mini-loader, IPL) stored in ROM Looks for OS loader program in a fixed location Loads OS loader (small) into RAM Transfers control to starting location of OS loader Loader loads the rest of the OS OS loads and executes user programs 52

53 53 Questions