part I, , Part I Introduction to Operating Systems First Semester, Year 2000 Wannarat Suntiamorntut Department of Computer Engineering, PSUWannarat Suntiamorntut

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Operating System Concepts * Intermediary between a user and computer hardware * Make computer system convenient to use * Computer hardware in an efficient manner

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut What is an Operating System? H hardware users operating systems Compiler Assembler text editor... database application programs

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut What is an Operating System? * Government * Resource allocator - CPU time, Memory space, file storage space, I/O device, network - de-allocate those resources * Virtual machine * Multiplexor, sharing of resource and protection * Provider of service provide common subroutines for programmer (window system, memory management) * Always run/load & embedded, usually called Kernel

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Why do we need an Operating System? User viewpoint Program environment viewpoint Efficiency viewpoint Economic viewpoint

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Services provide by OS Program creation Program execution Access to I/O devices Controlled access to files Error detection and response –hardware errors (e.g., memory error, device failures) –software errors (e.g., overflow, out of memory boundary) Accounting –collect usage statistics, monitor performance

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Typical services CPU scheduling: allocate computing time among several processes Memory management: allocate main memory among several processes Swapping: move processes and their data between main memory and secondary storage I/O device drivers: specialized code required to operate I/O devices File system: organize mass storage (disk) into files and directories

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Typical services Utilities: date/time, accounting, file copy, etc. Command interpreter: allow users to enter commands interactively System calls: allow user programs access to O.S. services Protection: keep processes from interfering with each other and system Communication & Resource sharing: allow users/processes to communicate (over networks) and share resources (e.g. laser printers, disks, etc.) Security: protect machines from intruders, worms and viruses

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Simple Batch Systems Turnaround = delay between job submission and job completion Spooling = Simultaneous Peripheral Operation on-line, as same as, large buffer. This systems use first-come,first serve algorithm. User Program Area OS

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Multiprogrammed Batched Systems OS Job 1 Job 2 Job 3 Job 4 Job scheduling switch process to execute, concern with memory management, process & device scheduling.

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Time-Sharing Systems Multitasking Multiple jobs are executed by the CPU switching. Interactive (hand-on) Provides online communication between the user and system. Time-shared OS allows many users to share computers simultaneously.

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Brief History of Operating Systems 1940's -- First Computers 1950's -- Batch Processing 1960's -- Multiprogramming (timesharing) 1970's -- Minicomputers & Microprocessors Late 1970's, 1980's -- Networking, Distributed Systems, Parallel Systems 1990's and Beyond -- PC’s, WWW, Mobile Systems

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut 1940’s... First Computers Computer dedicated to one user/programmer at a time. Program loaded manually by programmer, using console switches. Debugging using console lights. Advantages: –Interactive (user gets immediate response) Disadvantages: –Expensive machine idle most of time, because people are slow. –Programming & debugging are tedious. –Each program must include code to operate peripherals -- error prone, device dependencies.

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut 1950’s... Batch Processing User/programmer submits a deck of cards that describes a job to be executed. Jobs submitted by various users are sequenced automatically by a resident monitor. Tape drives available for batching of input and spooling of output. Advantages: –Computer system is kept busier. Disadvantages: –No longer interactive; longer turnaround time. –CPU is still idle for I/O-bound jobs.

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut 1960’s... Multiprogramming (Timesharing) The advent of the I/O processor made simultaneous I/O and CPU processing possible. CPU is multiplexed (shared) among a number of jobs -- while one job waiting for I/O, another can use CPU. Advantages: –Interactiveness is restored. –CPU is kept busy. Disadvantages: –Hardware and O.S. required become significantly more complex.

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut 1970’s... Minicomputer & Microprocessor Trend toward many small to mid-range personal computers, rather than a single mainframe. Early minicomputers and microprocessors were small, so there was some regression to earlier OS ideas. –e.g. DOS on PC is still essentially a batch system similar to those used in 1960, with some modern OS ideas thrown in (e.g., hierarchical file system). This trend is changing rapidly because of powerful new microprocessors. Also, the user interface became more important.

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Powerful workstations Local area networks (Ethernet) and long-distance network (Arpanet) Networks organized with clients and servers Decentralization of computing requires more communication (e.g., resource sharing) O.S. issues -- network communication protocols, data encryption, security, reliability, consistency of distributed data Late 1970’s, 1980’s.. Networking

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Parallel Computing (tera-flops) High-speed, long-distance communication links to send large amounts of data, including graphical, audio and video Electronic notebooks using wireless communication technologies World Wide Web Multimedia computers, powerful personal computers O.S. issues - Large heterogeneous systems, mobile computing. 1990’s and Beyond

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Parallel Systems Multiprocessor Systems (more than one processor) Advantage are - Increased throughput - work done in short time period - reliability

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Distributed Systems Distributed computation among several processors. Each processors communicates with high speed buses, Telephone line. Reason for building distributed systems : - resource sharing - computation speed up - Reliability - Communication

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Real - Time Systems Hard real-time system - Industrial control - Robotics - undersea exploration (Titanic) - Planetary Soft real-time system

part I, Department of Computer Engineering, PSUWannarat Suntiamorntut Next Class Discussion in “Computer System Structures” (Lesson 2 in Text Book)