Operating System Introduction -Compiled for MCA Ref: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc.

Content Introduction of Operating System Functions of operating system History of operating system Types of operating system Structure of operating system

What Is An Operating System? Lots of hardware !! One or more processors Main memory Disks Printers Various input/output devices Managing all these components requires a layer of software – the operating system

Where is the software? Where the operating system fits in.

The Operating System as an Extended Machine

The Operating System as a Resource Manager Allow multiple programs to run at the same time Manage and protect memory, I/O devices, and other resources Multiplexes (shares) resources in two different ways: In time In space

Functions of operating system Process management Process creation, deletion, suspension and resumption Process synchronization and inter process communication Process interactions – deadlock detection, avoidance and correction Mutitasking   Memory management Allocate and deallocate memory to process Manage multiple processes within the memory Manage the sharing of memory between processes Determine which processed to load when memory is available

Functions of operating system Storage Management Directory / File creation and deletion File system management File/directory manipulation Backup and achieve Free-space management Disk scheduling   I/O management Device driver installation Device interface and management

Functions of operating system Protection and security File attribute for accidental modification Provides policy for user Authentication Data encryption Firewall   Networking Provides different sets of protocols that are used for secure networking TCP/IP, FTP, POP, SMTP Interface CUI GUI Interactive

History of Operating Systems Generations: (1945–55) Vacuum Tubes (1955–65) Transistors and Batch Systems (1965–1980) ICs and Multiprogramming (1980–Present) Personal Computers, Tablets, Phones

Transistors and Batch Systems (1) Figure 1-3. An early batch system. (a) Programmers bring cards to 1401. (b)1401 reads batch of jobs onto tape.

Transistors and Batch Systems (2) Figure 1-3. (c) Operator carries input tape to 7094. (d) 7094 does computing. (e) Operator carries output tape to 1401. (f) 1401 prints output.

ICs and Multiprogramming MULTICS Timesharing CTSS (MIT) Multics UNix Figure 1-5. A multiprogramming system with three jobs in memory.

More third generation . Time Sharing (CTSS) Multics Unix Linux MULTICS Timesharing CTSS (MIT) Multics UNix .

Fourth generation . PCs Network Operating Systems Distributed Operating Systems MULTICS Timesharing CTSS (MIT) Multics UNix .

Multithreaded and Multicore Chips (a) A quad-core chip with a shared L2 cache. (b) A quad-core chip with separate L2 caches.

The Operating System Types Mainframe operating systems Big-thousands of disks…. Lots of jobs with lots of I/O Services-batch (payroll) transactions (airline reservations, timesharing (query database) Elderly-Unix, Linux replacing them

The Operating System Types:

The Operating System Types: Batch operating systems The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. Disadvantage: Lack of interaction between the user and the job. CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU. Difficult to provide the desired priority.

The Operating System Types: Server operating systems Workstations File, print, web servers BSD, Linux, Windows Multiprocessor operating systems Use multiple cores

The Operating System Types: PC operating systems-Linux, Mac, Windows Smart phone operating systems- Android, iPhone, Blackberry No hard disk Palm, Symbian popular OS’s Multiprogramming OS Run multiple program on single core Advantage: Reduce CPU idle time and utilize it Disadvantage: Question of security and integrity of user programs and data.

The Operating System Types: Real-Time OS- Data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as response time. Types: Hard real-time: Guarantee that critical tasks complete on time. Secondary storage is limited or missing with data stored in ROM. Virtual memory is almost never found.

The Operating System Types: Soft real-time: Soft real time systems are less restrictive. Have limited utility than hard real-time systems. Example: Multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers etc.

Operating Systems Structure Monolithic systems A main program that invokes the requested service procedure. A set of service procedures that carry out the system calls. A set of utility procedures that help the service procedures.

Monolithic Systems

Easy for error detection Layered Systems-THE operating system Components are organized and module are layered them from one top to next Module are not free to communicate directly without maintaining hierarchy Easy for error detection

Layered Systems-THE operating system Dijkstra’s the author

Layered Systems

Microkernels

Microkernels Small number of processes are allowed in the kernel Minimizes effects of bugs Don’t want bug in driver to crash system Put mechanism in kernel and policy outside the kernel Mechanism- schedule processes by priority scheduling algorithm Policy-assign process priorities in user space

Microkernels Structure of the MINIX 3 system.

Microkernels

Client-Server Model Divide operating kernel into several process I/O server, memory server, thread interface server, print server etc Servers run in user mode provide service when client demands

Client-Server Model The client-server model over a network.

Virtual Machines (1) The structure of VM/370 with CMS.

Virtual Machines (2) (a) A type 1 hypervisor. (b) A type 2 hypervisor.