Net 321 : Computer Operating System

1. Net 321 :Computer Operating System Lecture # 1 : Introduction Networks and Communication Department

2. Chapter 1: Introduction

3. Chapter 1: Introduction What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Kernel Data Structures Computing Environments

4. Objectives To describe the basic organization of computer systems To provide a grand tour of the major components of operating systems To give an overview of the many types of computing environments

5. Intro: What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware Operating system 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

6. 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

7. Four Components of a Computer System

8. The operating system’s Role Depends on the point of view • User View: • Single User (personal computer) • OS designed for ease of use , with some attention paid to performance and no paid for resource utilization. • Multiple User’s (mainframe or minicomputer) • OS designed to maximize resource utilization. • Workstations users connected to networks of other workstations and servers • OS designed to compromise between individual usability and resource utilization.

9. The operating system’s Role (cont.) • System View: • OS is a resource allocator • Manages all resources • Decides between conflicting requests for efficient and fair resource use • It is important when many users access the same mainframe or minicomputer • OS is a control program • Controls execution of programs to prevent errors and improper use of the computer • It is especially concerned with the operation and control of I/O devices.

10. Operating System Definition No universally accepted definition “The one program running at all times on the computer” is the kernel. Everything else is either a system program : whichassociated with the operating system but are not part of the kernel an application program: which include all programs not associated with the operating system An operating system is a software that manages the computer hardware, as well as providing an environment for application programs to run.

11. Computer Startup bootstrap programis loaded at power-up or reboot Typically stored in ROM or EPROM, generally known as firmware Initializes all aspects of system Loads operating system kernel and starts execution

12. Computer-System Organization • Computer-System Operation • Storage Structure • I/O Structure

13. Computer System Organization Computer-system operation One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles

14. Computer System Operation (cont.) Interrupt: • The occurrence of an event is usually signaled by an interrupt from either the hardware or the software. • Hardware interrupts by sending a signal to the CPU through system bus. • Software interrupts by executing a special operation called a system call. The interrupt is signal that gets the attention of the CPU and is usually generated when I/O is required. For example, hardware interrupts are generated when a key is pressed or when the mouse is moved. Software interrupts are generated by a program requiring disk input or output.

15. Computer-System Operation I/O devices and the CPU can execute concurrently Each device controller is in charge of a particular device type Each device controller has a local buffer CPU moves data from/to main memory to/from local buffers I/O is from the device to local buffer of controller Device controller informs CPU that it has finished its operation by causing an interrupt

16. Storage Structure Main memory – only large storage media that the CPU can access directly Randomaccess Typically volatile Secondary storage – extension of main memory that provides large nonvolatilestorage capacity

17. Storage Hierarchy Storage systems organized in hierarchy Speed Cost Volatility Caching – copying information into faster storage system; main memory can be viewed as a cache for secondary storage

18. Storage-Device Hierarchy

19. I/O Structure • each device controller is in charge of a specific type of device. • A device controller maintains some local buffer storage and a set of special-purpose registers. • OS have a device driver for each device controller. This device driver understands the device controller and presents a uniform interface to device to the rest of the operating system.

20. I/O Structure(cont.) • To start interrupt-driven I/O operation, • The device driver loads the appropriate registers within the device controller. • The device controller examines the contents of registers to determine what action to take. • The controller starts the transfer of 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. • The device driver returns control to the OS. What is the problem of this form?

21. I/O Structure (cont.) • Direct Memory Access (DMA) • 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

22. How a Modern Computer Works A von Neumann architecture

23. Computer-System Architecture • Most systems use a single general-purpose processor (PDAs through mainframes) • Most systems have special-purpose processors as well • Multiprocessors systems growing in use and importance • Also known as parallel systems, tightly-coupled systems • Advantages include • Increased throughput • Economy of scale • Increased reliability – fault tolerance • Two types • Asymmetric Multiprocessing (master-slave relationship) • Symmetric Multiprocessing (all processors are peers)

24. Symmetric Multiprocessing Architecture

25. A Dual-Core Design • Processors were originally developed with only one core. • The core is the part of the processor that actually performs the reading and executing of the instruction. Single-core processors can only process one instruction at a time • Dual-core processor contains two cores (Such as Intel Core Duo).

26. Operating System Structure • Multiprogramming needed for efficiency • Multiprogramming organizes jobs (code and data) so CPU always has one to execute. (Increase CPU Utilization.) • 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 Multiprogramming systems provide an environment in which the various system resources are utilized effectively, Not for user interaction with the computer system

27. Memory Layout for Multiprogrammed System

28. Uniprogramming • Processor must wait for I/O instruction to complete before preceding

29. Multiprogramming • When one job needs to wait for I/O, the processor can switch to the other job

30. Multiprogramming (cont.)

31. Operating System Structure (cont.) • Timesharing (multitasking) is logical extension of multiprogramming in which 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 • If processes don’t fit in memory, swapping moves them in and out to run • Virtual memory allows execution of processes not completely in memory

32. Time Sharing • Using multiprogramming to handle multiple interactive jobs • Processor’s time is shared among multiple users • Multiple users simultaneously access the system through terminals

33. Operating-System Operations • OS are interrupt driven. • Since the OS and the user share the HW and SW resources , we must sure that an error in user program could cause problems only for its running. • EX: process problems include infinite loop, this loop could prevent the correct operation of many other processors or the OS. • 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

34. Transition from User to Kernel Mode

35. Distributed Systems • Distributed systems allow users to share resources on geographically dispersed hosts connected via a computer network. • The basic types of networks are: • Local-area Network (LAN) connects computers within a room, a floor, or a building. • Wide-area Network (WAN) links building, cities or countries. • A network operating system • provides features such as file sharing across the network • and includes a communication scheme that allows different processes on different computers to exchange messages

36. Computing Environments • Traditional computing (Centralized computing) • Office environment • PCs connected to a network, terminals attached to mainframe or minicomputers providing batch and timesharing • Now portals allowing networked and remote systems access to same resources • Home networks • Used to be single system, then modems • Now firewalled, networked Centralized computing is computing done at a central location, using terminals that are attached to a central computer.

37. Computing Environments (Cont) • Client-Server Computing • Many systems now servers, responding to requests generated by clients • Compute-server provides an interface to client to request services (i.e. database) • File-server provides interface for clients to store and retrieve files

38. Peer-to-Peer Computing • Another model of distributed system • P2P does not distinguish clients and servers • Instead all nodes are considered peers • May each act as client, server or both • To participate in a P2P system, a node must join P2P network by: • Registers its service with centralized lookup service on network, or • Broadcast request for service and respond to requests for service via discovery protocol

39. End of Chapter 1