Introduction  What is an Operating System  What Operating Systems Do  How is it filling our life 1-1 Lecture 1

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  Use the computer hardware in an efficient manner  Make the computer system convenient to use 1-2 Lecture 1

What is a Computer System?  Computer system structure can be divided into four components:  Hardware – provides basic computing resources CPU, memory, I/O devices  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  Operating system – “the manager of the above three” Controls and coordinates use of hardware among various applications and users 1-3 Lecture 1

Computer System and how OS fits into it 1-4 Lecture 1

Operating System Definition  From system point of view:  OS is a resource allocator  Manages all resources  Decides between conflicting requests for efficient and fair resource use  OS is a control program  Controls execution of programs to prevent errors and improper use of the computer 1-5 Lecture 1

How OS evolved  Mainframe Systems  One of the earliest computer systems  Huge computers  Very simple systems  Can process one job after another  Jobs were fed with punch cards  Operators sort jobs into batches  Also known as Batch Systems  Mainframe systems have severe efficiency problem  WHY? Image courtesy: Lecture 1

Mainframe OS – severe disadvantages  Mainframe Systems  Process one job after another  Jobs were fed with punch cards  CPU works in microseconds range  I/O system very slow  Approx cards/min.  20 cards/sec.  CPU is almost always idle!!!  It was needed to keep multiple jobs ready so that CPU does not become idle…how?  Introduction of disk technology changed the complete OS history Image courtesy: Lecture 1

Multiprogrammed Systems  Multiprogramming 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  How to achieve this?  Disk technology helped us to keep multiple jobs in job pool (Disk)  A subset of total jobs in system is kept in memory  One job selected and executed  When it has to wait (I/O for example), OS switches to another job  Multiprogrammed introduced two novel challenges  Job scheduling  Memory management 1-8 Lecture 1

Time-Sharing Systems  Time-sharing systems are logical extension of multiprogrammed systems  Also known as multitasking  Each user has at least one program executing in memory  process  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  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 1-9 Lecture 1

Multiprocessor Systems  Most systems use a single general-purpose processor (PDAs through mainframes)  Multiprocessor systems growing in use and importance  Also known as parallel systems, tightly-coupled systems  Advantages include 1.Increased throughput 2.Economy of scale 3.Increased reliability – graceful degradation or fault tolerance  Two types 1.Asymmetric Multiprocessing 2.Symmetric Multiprocessing 1-10 Lecture 1

Symmetric Multiprocessing Architecture 1-11 Lecture 1

A Dual-Core Design 1-12 Lecture 1

Shift to Distributed Systems Client-Server Computing Distributed systems over the network 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 1-13 Lecture 1

Peer-to-Peer Systems  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  Node must join P2P network Registers its service with central lookup service on network, or Broadcast request for service and respond to requests for service via discovery protocol  Examples include Napster and bitTorrent 1-14 Lecture 1

Change in Computing Environments  Traditional computing  Office environment Earlier, 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 Earlier, used to be single system, then modems Now, firewalled, networked 1-15 Lecture 1