OPERATING SYSTEMS Prof. Sujata Rao Lesson 3

Agenda 1. What is an operating system? 2. How have operating systems evolved? 3. Functions of Operating System ? 4. Types of Operating System ? 5. Why study operating systems? Introduction to Operating Systems

1. What is an Operating System? Connector between an application & hardware Software that converts hardware into a useful form for applications To define precisely… Users Hardware Operating System Applications compilers databases word processors CPU memory I/O devices

Definition Set of programs containing instructions that co-ordinate all the activities among  computer hardware resources and  the application software which enables the hardware to conduct the essential activity

Roles of an OS Role #1  Provide standard Library (ie. abstract resources) Role #2  Resource coordinator (ie. manager)

Role #1 Provide standard Library (ie. abstract resources) Abstract Resource?  e.g., CPU, memory, disk etc Advantages of standard library  Allow applications to reuse common facilities  Make different devices of similar type look the same  Provide higher-level abstractions Challenges  What are the correct abstractions?  How much of hardware should be exposed?

Role #2: Resource coordinator (ie. manager) Advantages of resource coordinator  Virtualizes resource so multiple users or applications can share  Protect applications from one another  Provide efficient and fair access to resources Challenges  What are the correct mechanisms?  What are the correct policies?

OS Functionality ? OS must adapt to both user expectations and technology changes Change abstractions provided to users Change algorithms to implement those abstractions Change low-level implementation to deal with hardware Current operating systems driven by evolution

2. Evolution of the OS Two distinct phases of history  Phase 1: Expensive Computers Goal: Use computer’s time efficiently Maximize throughput (I.e., jobs per second) Maximize utilization (I.e., percentage busy)  Phase 2: Inexpensive Computers Goal: Use people’s time efficiently Minimize response time

First commercial systems 1950s Hardware  Enormous, expensive, and slow  Input/Output: Punch cards and line printers Goal of OS  Get the hardware working  Single operator/programmer/user runs and debugs interactively OS Functionality  Standard library only (no sharing or coordination of resources)  Monitor that is always resident; transfer control to programs

First commercial systems Advantages  Worked and allowed interactive debugging Problems  Inefficient use of hardware (throughput and utilization)

O/s for Batch Processing Goal of OS: Better throughput and utilization Batch: Group of jobs submitted together  Operator collects jobs; orders efficiently; runs one at a time Advantages  Amortize setup costs over many jobs  Operator more skilled at loading tapes  Keep machine busy while programmer thinks  Improves throughput and utilization Problems  User must wait until batch is done for results  Machine idle when job is reading from cards and writing to printers

O/s for Spooling Goal of OS  Improve performance by overlapping I/O with CPU execution Hardware  Mechanical I/O devices much slower than CPU  Read 17 cards/sec vs. execute 1000s instructions/sec

Spooling: Simultaneous Peripheral Operations On-Line 1. Read card punches to disk 2. Compute (while reading and writing to disk) 3. Write output from disk to printer OS Functionality  Buffering and interrupt handling Problem  Machine idle when job waits for I/O to/from disk

Multiprogrammed Batch Systems Observation: Spooling provides pool of ready jobs Goal of OS  Improve performance by always running a job  Keep multiple jobs resident in memory  When job waits for disk I/O, OS switches to another job OS Functionality  Job scheduling policies  Memory management and protection Advantage: Improves throughput and utilization Disadvantage: Machine not interactive

Inexpensive Peripherals 1970’ s Hardware  Expensive mainframes, but inexpensive keyboards and monitors  Enables text editors and interactive debuggers Goal of OS  Improve user’s response time OS Functionality  Time-sharing: switch between jobs to give appearance of dedicated machine  More complex job scheduling  Concurrency control and synchronization Advantage  Users easily submit jobs and get immediate feedback

Inexpensive Personal Computers 1980s Hardware  Entire machine is inexpensive  One dedicated machine per user Goal of OS  Give user control over machine OS Functionality  Remove time-sharing of jobs, protection, and virtual memory Advantages  Simplicity  Works with little main memory  Machine is all your own (performance is predictable) Disadvantages  No time-sharing or protection between jobs

Inexpensive, Powerful Computers 1990s + Hardware  PCs with increasing computation and storage  Users connected to the web Goal of OS  Allow single user to run several applications simultaneously  Provide security from malicious attacks  Efficiently support web servers OS Functionality  Add back time-sharing, protection, and virtual memory

Current Systems Conclusion: OS changes due to both hardware and users Current trends  Multiprocessors  Networked systems  Virtual machines OS code base is large  Millions of lines of code  1000 person-years of work Code is complex and poorly understood  System outlives any of its builders  System will always contain bugs  Behavior is hard to predict, tuning is done by guessing

OS Components Kernel: Core components of the OS Process scheduler  Determines when and for long each process executes Memory manager  Determines when and how memory is allocated to processes  Decides what to do when main memory is full File system  Organizes named collections of data in persistent storage Networking  Enables processes to communicate with one another

3. Functions of an O/s i. Providing a user interface a) Command Line Interface b) Graphic User Interface ii. Managing Programs a) Single -User Multitasking b) Multi-User & Multi Tasking iii. Managing Memory  Swapping, Paging & Thrashing iv. Scheduling jobs - Spooling

3. Functions of an O/s v. Configuring Devices- with the help of device drivers vi. Establishing an internet connection vii. Controlling a Network viii. Monitoring Performances ix. Providing File Management x. Administering security

4. Types of O/s Stand Alone O/s A complete O/s which works on a Desktop, Laptop, Palmtop, Mobile etc. They can work with or without another operating system Network O/s O/s that is made to support a network of computers. Embedded O/s O/s for small devices enabled for wireless communication

4. Stand Alone O/s Dos Windows Mac Unix Linux

4. Network O/s Windows NT Windows 2003 family Unix Linux Solaris Novell Netware

Embeded O/s Windows CE ( windows for Communication & Entertainment) Palm O/s Blackberry Embeded Linux Symbian O/s

5. Why study Operating Systems? Build, modify, or administer an operating system Understand system performance  Behavior of OS impacts entire machine  Challenge to understand large, complex system  Tune workload performance  Apply knowledge across many areas Computer architecture, programming languages, data structures and algorithms, and performance modeling

DOS Command Screen Command Line DOS Prompt

Internal DOS Commands.. A: - Change current directory path to the floppy disk drive C: - Change current directory path to the hard disk drive DIR - Display current directory (show all files and sub- directories). MD - Make a new directory, eg: MD C:\ CD - Change current directory, eg. CD C:\

The Command Line Two commands, “time” and “date”, were entered with primitive results…

GUI - Notice the difference… …when one click on the taskbar gives you this

DOS commands COPY - Copy file(s) from one place to another. Del - Delete/erase a file Any other text on the input line after the file name, is passed to the program. Ex. "Copy help.txt help.bak",  the text, "help.txt” & “ help.bak" is passed to the copy program which will in this case use it to specify source and destination files for copy function