Operating Operating SystemsSystems

OverviewOverview

What is an Operating System (OS)What is an Operating System (OS) What Operating Systems do.What Operating Systems do. Operating system issuesOperating system issues Kinds of Operating SystemsKinds of Operating Systems

What is an OS?What is an OS?

““An operating system is a layer of An operating system is a layer of software which takes care of technical software which takes care of technical aspects of a computer's operation. It aspects of a computer's operation. It

shields the user of the machine from the shields the user of the machine from the low-level details of the machine's low-level details of the machine's operationoperation and provides frequently and provides frequently

needed facilities” needed facilities”

Taken fromTaken from

http:// http://www.iu.hio.nowww.iu.hio.no

What is an OS? What is an OS?

An Operating System makes the An Operating System makes the computing power available to users computing power available to users by controlling the hardwareby controlling the hardware

Without an OS, computers would Without an OS, computers would only be able to run one program at a only be able to run one program at a timetime

Programs must run according to the Programs must run according to the rules of the OSrules of the OS

What Operating Systems What Operating Systems do:do:

1.1. ProvideProvide software software for driving the for driving the hardware of the computer hardware of the computer

2.2. Implement a Implement a file systemfile system which which provides a way of organizing files provides a way of organizing files logicallylogically

3.3. Distribute computer resources Distribute computer resources between applicationsbetween applications

1. Software that Runs 1. Software that Runs HardwareHardware

A driver is software that designed to A driver is software that designed to run a piece of hardwarerun a piece of hardware Ex: Printer, fancy keyboard, scannerEx: Printer, fancy keyboard, scanner

New drivers are built into the OS. New drivers are built into the OS. This is why it is often necessary to This is why it is often necessary to restart your computer when a driver restart your computer when a driver is addedis added

2. File System2. File System

The OS must save files in a logical The OS must save files in a logical efficient wayefficient way Hard drive, floppy diskHard drive, floppy disk Through FAT (File Allocation Table)Through FAT (File Allocation Table)

Recall, FAT32 vs FAT16Recall, FAT32 vs FAT16 32 bit addressing means each section of 32 bit addressing means each section of

memory is broken up into 2^32 memory is broken up into 2^32 individual addressing locationsindividual addressing locations

Much faster to find a file!Much faster to find a file!

File Systems: NTFSFile Systems: NTFS

NTFS is the “NT File System” NTFS is the “NT File System” developed by Microsoftdeveloped by Microsoft

Faster and more efficient.Faster and more efficient. XP and Vista would use NTFSXP and Vista would use NTFS

RAMRAM

OS is also responsible for memory OS is also responsible for memory allocation in RAM allocation in RAM

The OS itself stays in RAM while the The OS itself stays in RAM while the computer is oncomputer is on

OS controls what is moved into and OS controls what is moved into and out of RAMout of RAM

Virtual MemoryVirtual Memory

Several programs can’t fit in main Several programs can’t fit in main memory so what happens?memory so what happens?

Virtual memory is parts of active Virtual memory is parts of active programs stored on the hard drive.programs stored on the hard drive. EX: I’ve got Windows XP running, MS Word, EX: I’ve got Windows XP running, MS Word,

3 Explorer Windows one being active3 Explorer Windows one being active Rather then not letting you open more Rather then not letting you open more

programs the OS will run them using programs the OS will run them using Virtual MemoryVirtual Memory

3. Distributing Computer 3. Distributing Computer ResourcesResources

The CPU can only do one thing at a The CPU can only do one thing at a time. Fortunately it can do billions of time. Fortunately it can do billions of things per second…things per second…

The OS is responsible for giving CPU The OS is responsible for giving CPU time to currently running applications.time to currently running applications.

The OS also makes sure two The OS also makes sure two applications don’t try accessing the applications don’t try accessing the same piece of hardware at the same same piece of hardware at the same time.time.

2 OS Issues2 OS Issues

Concurrency control (multi-tasking)Concurrency control (multi-tasking) DeadlockDeadlock

Concurrency ControlConcurrency Control

Several programs running at a timeSeveral programs running at a time Means Sharing CPU timeMeans Sharing CPU time

While a program waits for an I/O While a program waits for an I/O operation another program can use operation another program can use the CPUthe CPU

DeadlockDeadlock Program A wants to copy from disk1 to Program A wants to copy from disk1 to

disk2 and takes control of disk1disk2 and takes control of disk1

Program B wants to copy from disk2 to Program B wants to copy from disk2 to disk1 and takes control of disk2disk1 and takes control of disk2

Program A must wait until program B Program A must wait until program B releases disk2 and program B must wait releases disk2 and program B must wait until program A releases disk1until program A releases disk1

Programs A and B will wait forever!Programs A and B will wait forever!

Deadlock PreventionDeadlock Prevention

OS must have a systematic way of OS must have a systematic way of controlling program execution controlling program execution

This is a very complex problemThis is a very complex problem One simple not very efficient One simple not very efficient

solution is to have programs solution is to have programs “timeout”, in our example program A “timeout”, in our example program A would timeout first and release disk would timeout first and release disk 1 and try again shortly 1 and try again shortly

Kinds of Operating Kinds of Operating SystemsSystems

What’s the best?What’s the best? Windows=Microsoft =monopoly!!!Windows=Microsoft =monopoly!!!

Success due to???Success due to??? Other alternatives:Other alternatives:

Mac- I’ve never met a sad Mac userMac- I’ve never met a sad Mac user Linux/Unix- Small very efficient, maybe Linux/Unix- Small very efficient, maybe

less intuitiveless intuitive

Work on OS AssignmentWork on OS Assignment