Operating Systems Course 2 nd semester 2016/2017 Chapter 1: Introduction

Transcription

1 Operating Systems Course 2 nd semester 2016/2017 Chapter 1: Introduction Lecturer: Eng. Mohamed B. Abubaker Note: Adapted from the resources of textbox Operating System Concepts, 9 th edition

2 What is an Operating System (OS)? A program that manages a computer s hardware. A program that acts as an intermediary between the computer user and the computer hardware. OS goals: Execute user programs and make solving user problems easier Make the computer system convenient to use Use the computer hardware in an efficient manner 2

3 Computer System Structure Computer system can be divided into four components: Hardware provides basic computing resources: CPU, memory, I/O devices Operating system: Controls and coordinates use of hardware among various applications and users Application programs define the ways in which the system resources are used to solve the computing problems of the users: Word processors, compilers, web browsers, database systems, video games Users: People, machines, other computers 3

4 Abstract view of the components of a computer system 4

5 What Operating Systems Do OS is similar to a government. To understand what OS do, we explore OS from two viewpoints: User View System View 5

6 User View (1/2) PC: single user OS is designed for ease of use, with some attention paid to performance and non paid to resource utilization. Mainframe or minicomputer: User share resources OS is designed to maximize resource utilization 6

7 User View (2/2) Workstations and servers: OS is designed to compromise between individual usability and resource utilization. Handheld computers: Such as smartphones OS is designed to be optimized for usability and battery life Embedded computers: Such in home devices and automobiles. Designed to run without user intervention 7

8 System View OS is the program most intimately involved with hardware OS can be viewed as: Resource allocator: Manages all resources: CPU, memory, file storage, I/O devices, Decides between conflicting requests for efficient and fair resource use Control program: Manages the execution of user programs to prevent errors and improper use of the computer 8

9 Defining Operating Systems We have no completely adequate definition of an OS A simple viewpoint is that Everything a vendor ships when you order an operating system A more common definition is that OS is the one program running at all times on the computer usually called the kernel. There are other types of programs: System programs Application programs 9

10 Computer-System Operation (1/3) A modern general-purpose computer system consists of: 10

11 Computer-System Operation (2/3) For a computer to start running: Bootstrap program is loaded at power up or rebooted Typically stored in ROM or EPROM, known by the general term firmware Initializes all aspects of the system from CPU registers to device controllers to memory Locates the OS kernel and load it in into memory 11

12 Computer-System Operation (3/3) Once the kernel is loaded and executing, it start providing services to the system and its users. Some services are provided outside of the kernel By system programs that are loaded into memory at boot time to become system processes or system daemons. On UNIX, the first system process is init and it starts many other daemons Once the system is fully booted, the system waits for some event to occur 12

13 Interrupt The occurrence of an event is signaled by an interrupt from either Hardware or Software. Device controller informs CPU that it has finished its operation by causing an interrupt Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines Interrupt architecture must save the address of the interrupted instruction A trap or exception is a software-generated interrupt caused either by an error or a user request An operating system is interrupt driven 13

14 Interrupt Handling The operating system preserves the state of the CPU by storing registers and the program counter Determines which type of interrupt has occurred: polling vectored interrupt system Separate segments of code determine what action should be taken for each type of interrupt 14

15 Interrupt Timeline 15

16 Storage Structure 16

17 Storage Definitions and Notation 17

18 I/O Structure (1/2) A general-purpose computer system consists of CPUs and multiple device controllers that are connected through a common bus. The device controller is responsible for moving the data between the peripheral devices that it controls and its local buffer storage. The OS has a device driver for each device controller to manage I/O: Device driver provides uniform interface between controller and kernel 18

19 I/O Structure (2/2) Device controller examines the contents of registers to determine what action to take. Controller transfers data from the device to its local buffer. Once the transfer of data is complete, the device controller informs the device driver via an interrupt that it has finished its operation. 19

20 Direct Memory Access Structure Used for high-speed I/O devices able to transmit information at close to memory speeds Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention Only one interrupt is generated per block, rather than the one interrupt per byte 20

21 How a Modern Computer Works 21

22 Computer-System Architecture A computer system can be categorized according to the number of generalpurpose processors used: Single-Processor Systems Multiprocessors Systems Clustered Systems 22

23 Single-Processor Systems There is one main CPU capable of executing a general-purpose instruction set. Almost all single-processor systems have other special-purpose processors as well. 23

24 Multiprocessor Systems Such systems have two or more processors in close communication. Also known as parallel systems, tightly-coupled systems, multicore systems Three main advantages: Increased throughput Economy of scale Increased reliability Two Types: Asymmetric multiprocessing Symmetric multiprocessing 24

25 Asymmetric Multiprocessing (AMP) A boss processor controls the systems A boss-worker relationship The boss processors schedules and allocate work to the worker processors 25

26 Symmetric Multiprocessing (SMP) More common All processors are peers Each processor performs all tasks within the OS Windows, Linux, Mac 26

27 27

28 Multicore Multiple computing cores on a single chip They can be more efficient than multiple chips with single core: on-chip communication faster then between chip communication One chip with multiple cores uses less power than multiple single-core chips 28

29 Dual-core design 29

30 Clustered Systems Like multiprocessors systems, but multiple systems working together. Loosely coupled Provide high availability Provide high performance computing Technique known as parallelization. 30

31 General Structure of a Clustered System 31

32 Operating System Structure (1/2) Multiprogramming (Batch system) needed for efficiency Single user cannot keep CPU and I/O devices busy at all times Multiprogramming organizes jobs (code and data) so CPU always has one to execute A subset of total jobs in system is kept in memory One job selected and run via job scheduling When it has to wait (for I/O for example), OS switches to another job 32

33 Operating System Structure (2/2) Time sharing (multitasking) is logical extension of multiprogramming CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing Response time should be < 1 second Each user has at least one program executing in memory process If several jobs ready to run at the same time CPU scheduling Virtual memory allows execution of processes not completely in memory 33

34 Memory Layout for Multiprogramming System 34

35 Operating System Operations Interrupt (hardware and software) Hardware interrupt by one of the devices Software interrupt (exception or trap): Software error (e.g., division by zero) Request for operating system service 35

36 Dual-Mode & Multi-Mode Operations Dual-mode operation allows OS to protect itself and other system components User mode and kernel mode Mode bit provided by hardware Provides ability to distinguish when system is running user code or kernel code Some instructions designated as privileged, only executable in kernel mode System call changes mode to kernel, return from call resets it to user Increasingly CPUs support multi-mode operations i.e. virtual machine manager (VMM) mode for guest VMs 36

37 Transition from User to Kernel Mode 37

38 Timer Timer is used to prevent a user program to get stuck in an infinite loop A timer is set to interrupt the computer after a specified period. Period may be fixed or variable 38

39 END 39