OS1-1 Chapter 1 Introduction

OS1-2 Introduction What is an Operating System? Mainframe Systems Desktop Systems Multiprocessor Systems Distributed Systems Clustered Systems Real -Time Systems Handheld Systems Computing Environments

OS1-3 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.

OS1-4 Computer System Components 1.Hardware – provides basic computing resources (CPU, memory, I/O devices). 2.Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3.Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4.Users (people, machines, other computers).

OS1-5 Operating System Four components of a computer system Users People, machines, other computers,... Applications (use resource to solve problems) Compilers, database systems, games, business programs,... Operating System (resource allocator) Hardware (resource) CPU, memory, I/O devices,...

OS1-6 Operating System Application Programs User 1 User 2 User 3 User n Compiler Assember Text Editor Browser Fig. 1.1 Computer Hardware

OS1-7 Operating System Definitions Resource allocator – manages and allocates resources. Control program – controls the execution of user programs and operations of I/O devices. Kernel – the one program running at all times (all else being application programs).

OS1-8 Goals of OS Primary-- convenience  make the computer system convenient to use Secondary-- efficiency  use the computer hardware in an efficient manner The two goals are contradictory sometimes In the past, the secondary goal is more important.

OS1-9 Mainframe: Batch Systems Main job of early OS: automatically transfer control from one job to the next. (resident in memory) To speed up processing, jobs with similar needs were batched together and were running through the computer as a group. A batch operating system Programmers submit jobs (program, data, control cards) Operator sort jobs into batches with similar requirements (Fortran, Cobol) OS transfers control from one job the the next.

OS1-10 program to be compiled data for the program $END $RU N $LOAD $FNT $JOB

OS1-11 Memory Layout for a Simple Batch System

OS1-12 Lack of interaction between the user and the job while that job is executing. CPU is often idle  I/O devices: card reader/printer  I/O speed << CPU speed (at least 1:1000) Introduction of Disk technology  Spooling (Simultaneous Peripheral Operation On-Line)  I/O is done with no CPU intervention  CPU just needs to be notified when I/O is done

OS1-13 CPU Card Reader Line Printer Disk Spooling

OS1-14 Spooling is also used for processing data at remote sites (CPU sends/reads data to/from remote printer/card-reader via communication paths). Spooling overlaps the I/O of one job with the computation of other jobs.  The spooler may be reading the input of one job while printing the output of a different job. By overlaps, spooling keeps both the CPU and the I/O devices working at much higher rates.

OS1-15 Mainframe: Multiprogramming Batched Systems Spooling provides an important data structure: a job pool, which contains jobs waiting on disk, ready to run. Job scheduling becomes possible: OS can select which job to run next, to increase CPU utilization. The most important aspect of job scheduling is the ability to multiprogram : OS keeps several jobs in memory at a time. Multiprogramming organizes jobs such that CPU always has one to execute. (When one job is waiting for I/O, CPU switches to another.)

OS1-16 Multiprogramming Systems Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them.

OS1-17 OS Features Needed for Multiprogramming I/O routine supplied by the system. Memory management – the system must allocate the memory to several jobs. CPU scheduling – the system must choose among several jobs ready to run. Allocation of devices.

OS1-18 Operating System Job 1 Job 2 Job 3 Job 4 CPU Job Scheduling CPU Scheduling Job pool

OS1-19 Mainframe: Time-Sharing Systems Disadvantages of a multiprogrammed batched systems No interaction with users: users must set up control cards for all possible outcomes. Statically debugging: long turnaround time inhibits experimentation. (But, it instills good discipline of writing/testing) An interactive (or hand-on) system: allows on- line communication between users and the system. (Usually, keyboard/screen are used. Users can see results immediately.)

OS1-20 Time-sharing (or multi-tasking): an extension of multiprogramming. CPU switches among jobs frequently such that users may interact with programs. Switch job when  finish  waiting I/O  a short period of time Early OS: single user, interactive Batch: good CPU utilization, no interaction Time-sharing: interaction, reasonable cost Combine: Batch + Time sharing (IBM OS/360)

OS1-21 Time-Sharing Systems – Interactive Computing The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). A job swapped in and out of memory to the disk. On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “ control statement ” from the user ’ s keyboard. On-line system must be available for users to access data and code.

OS1-22 Time-sharing System CPU Scheduling and multiprogramming provide each user with a small portion of a time-shared computer. CPU-bound and I/O-bound process Memory management and Protection Virtual memory File system, Disk management Concurrent execution Process synchronization and Deadlock

OS1-23 Migration of OS Concepts and Features

OS1-24 The Movement of OS MULTICS ( MIT) for GE 645 UNIX (Ken Thompson, 1970 Bell Lab) for PDP-11, C-language UNIX-like OS: System V, XENIX, BSD, Solaris Workstation: SPARCstation, RS/6000, NT PC: Windows, Linux, … Hand-held: Palm, Windows CE, … Embedded Systems

OS1-25 Desktop Systems Personal computers – computer system dedicated to a single user. I/O devices – keyboards, mice, display screens, small printers. User convenience and responsiveness. Can adopt technology developed for larger operating system ’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features. May run several different types of operating systems (Windows, MacOS, UNIX, Linux)

OS1-26 Personal-Computer Systems PCs appeared in the 1970s, instead of maximizing CPU and peripheral utilization, the systems opt for maximizing user convenience and responsiveness. MS-DOS, OS/2, Mac OS, Windows, Linux, … GUI Lack of file protection at first: destroy data, system or even worldwide networks via virus mechanisms. LAN, Internet and browser

OS1-27 Parallel Systems Multiprocessor systems with more than on CPU in close communication. Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. Advantages of parallel system: Increased throughput Economical Increased reliability  graceful degradation  fail-soft systems

OS1-28 Parallel Systems (Cont.) Symmetric multiprocessing (SMP) Each processor runs and identical copy of the operating system. Many processes can run at once without performance deterioration. Most modern operating systems support SMP, Solaris 2, … Asymmetric multiprocessing Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. More common in extremely large systems

OS1-29 Symmetric Multiprocessing Architecture

OS1-30 Distributed Systems Distribute the computation among several physical processors. Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high- speed buses or telephone lines. Advantages of distributed systems. Resources Sharing Computation speed up – load sharing Reliability Communications

OS1-31 Distributed Systems (cont) Requires networking infrastructure. Local area networks (LAN) or Wide area networks (WAN) May be either client-server or peer- to-peer systems.

OS1-32 General Structure of Client- Server

OS1-33 Clustered Systems Clustering allows two or more systems to share storage. Provides high reliability. Asymmetric clustering: one server runs the application while other servers standby. Symmetric clustering: all N hosts are running the application.

OS1-34 Real-Time Systems Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. Well-defined fixed-time constraints. Real-Time systems may be either hard or soft real-time.

OS1-35 Real-Time Systems (Cont.) Hard real-time: Guarantees that the critical tasks complete on time Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM) Conflicts with time-sharing systems, not supported by general-purpose operating systems. No general-purpose hard real-time systems exist. Soft real-time A critical real-time task gets priority over other tasks, and retains that priority until it completes. Kernel delays need to be bounded; Limited utility in industrial control of robotics Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

OS1-36 Handheld Systems Personal Digital Assistants (PDAs) Cellular telephones Issues: Limited memory Slow processors Small display screens.

OS1-37 Computing Environments Traditional computing Web-Based Computing Embedded Computing