Computing and the WebComputing and the WebOperating SystemsOperating Systems

OverviewOverview What is an Operating SystemWhat is an Operating System Booting the ComputerBooting the Computer User InterfacesUser Interfaces Files and File ManagementFiles and File Management Input and Output of InformationInput and Output of Information Memory Limitations: Cache and Virtual MemoryMemory Limitations: Cache and Virtual Memory Context Switching and MultitaskingContext Switching and Multitasking Operating Systems for the Networked WorldOperating Systems for the Networked World

What is an Operating What is an Operating System?System?A collection of programs that manages and controls A collection of programs that manages and controls software, and coordinates the various hardware software, and coordinates the various hardware components to perform tasks requested by the usercomponents to perform tasks requested by the user

Isolate the hardware Isolate the hardware from users and from users and direct manipulation direct manipulation by applicationsby applications

What if the OS wasn’t there?What if the OS wasn’t there? Programs “poked” into RAM via switchesPrograms “poked” into RAM via switches First program loaded “read” other programsFirst program loaded “read” other programs Next program added “device support”Next program added “device support” Devices could then be used to read in larger Devices could then be used to read in larger

programs like BASICprograms like BASIC

Overall process was tedious and slow (could Overall process was tedious and slow (could take up to 30 minutes)take up to 30 minutes)

You wouldn’t want to shut off the computerYou wouldn’t want to shut off the computer

BIOS to the rescueBIOS to the rescue BIOS is the Basic Input Output SystemBIOS is the Basic Input Output System Collection of programsCollection of programs Provides the capability of Provides the capability of

communicating with peripheral devicescommunicating with peripheral devices– KeyboardKeyboard– Disk drivesDisk drives– MonitorMonitor

Allows the rest of the operating system Allows the rest of the operating system to be read in from the disk driveto be read in from the disk drive

Stored in ROM so it is always thereStored in ROM so it is always there

What is an Operating What is an Operating System?System? A collection of programs that carry out A collection of programs that carry out

six basic functionssix basic functions– Booting the ComputerBooting the Computer– Provides the User InterfaceProvides the User Interface– Provides File ManagementProvides File Management– Handles Input and Output OperationsHandles Input and Output Operations– Manages MemoryManages Memory– Provides Context Switching & MultitaskingProvides Context Switching & Multitasking

Examples of Operating Systems:Examples of Operating Systems:Windows (98, NT, ME, XP), MS-DOS, CPM, Mac OS X, UNIX, OS/2, Windows (98, NT, ME, XP), MS-DOS, CPM, Mac OS X, UNIX, OS/2,

LINUX, VMS, PALM OS, SOLARISLINUX, VMS, PALM OS, SOLARIS

Booting the ComputerBooting the Computer Process of automatically running a Process of automatically running a

program in ROM which in turn loads the program in ROM which in turn loads the operating system into RAM and turns operating system into RAM and turns control over to it.control over to it.

Cold Boot – booting up when the power Cold Boot – booting up when the power was originally offwas originally off

Warm Boot – booting up when the Warm Boot – booting up when the power was originally on (re-booting)power was originally on (re-booting)– Gets a fresh copy of the operating systemGets a fresh copy of the operating system

Multiple Operating Systems – Multiple Operating Systems – partitioning the hard drive for each OSpartitioning the hard drive for each OS

User InterfacesUser Interfaces The user interface is the part of the Operating The user interface is the part of the Operating

System that the user sees and interacts withSystem that the user sees and interacts with Different types of interfaces for different purposesDifferent types of interfaces for different purposes

– GUIGUI– CLICLI

GUI – Graphical user interfaceGUI – Graphical user interface– Mouse oriented and utilizes icons and buttonsMouse oriented and utilizes icons and buttons– Allows symbolic manipulation of programs and filesAllows symbolic manipulation of programs and files

CLI – Command line interfaceCLI – Command line interface– Instructions are given by typing commands on the Instructions are given by typing commands on the

keyboardkeyboard– Requires technical understanding of commandsRequires technical understanding of commands– Not user friendly or intuitiveNot user friendly or intuitive

Files and File ManagementFiles and File Management A file is a collection of [data] that is A file is a collection of [data] that is

treated as a single unittreated as a single unit– A pictureA picture– A spread sheetA spread sheet– A documentA document– A programA program

A file has a unique nameA file has a unique name– Filename Filename .. Extension Extension

Extensions are used to associate files Extensions are used to associate files with programswith programs

Files and File ManagementFiles and File Management There are two basic types of file There are two basic types of file

systemssystems– Flat file structureFlat file structure– Hierarchical file structureHierarchical file structure

Flat file structureFlat file structure– Organizes files in one flat listOrganizes files in one flat list– No subdivision or grouping possibleNo subdivision or grouping possible– Like dumping all of your papers in a pile on Like dumping all of your papers in a pile on

the top of your deskthe top of your desk– Difficult to manage and keep track of filesDifficult to manage and keep track of files

Files and File ManagementFiles and File Management Hierarchical file structureHierarchical file structure

– Organizes files in a tree like structureOrganizes files in a tree like structure– Subdivision is achieved via subdirectories Subdivision is achieved via subdirectories

(usually depicted as folders)(usually depicted as folders)– Similar to filing cabinets with drawers and Similar to filing cabinets with drawers and

folders within themfolders within them– Easy to manage and keep track of filesEasy to manage and keep track of files– The folders become part of the naming The folders become part of the naming

convention for the fileconvention for the file

C:\Windows\System32\Regedit.exeC:\Windows\System32\Regedit.exe

Input and Output SupportInput and Output Support I/O support provides basic support to I/O support provides basic support to

read and write information to peripheral read and write information to peripheral devicesdevices

Specialized devices may require special Specialized devices may require special software called a device driversoftware called a device driver– Device drivers are usually provided by the Device drivers are usually provided by the

manufacturer of the specialized hardwaremanufacturer of the specialized hardware– Device drivers provide enhanced features that Device drivers provide enhanced features that

the operating system doesn’t know aboutthe operating system doesn’t know about I/O support also provides error handling I/O support also provides error handling

in case of device failuresin case of device failures

Memory ManagementMemory Management Real vs Virtual MemoryReal vs Virtual Memory Computers have a physical amount of Computers have a physical amount of

RAMRAM All memory in the computer is “owned” All memory in the computer is “owned”

by the operating systemby the operating system The operating system allocates memory The operating system allocates memory

to programs as they need itto programs as they need it The operating system reclaims memory The operating system reclaims memory

when programs are done with itwhen programs are done with it

Memory ManagementMemory Management Memory “some” PC after boot upMemory “some” PC after boot up

Memory ManagementMemory Management The user starts up a web browserThe user starts up a web browser

Memory ManagementMemory Management The user starts up several more programsThe user starts up several more programs

Memory ManagementMemory ManagementThe user wants to start a program that is 35M, but only 20M is freeThe user wants to start a program that is 35M, but only 20M is free

Memory ManagementMemory ManagementWindows will clear out 15M of memory that hasn’t been used in a while and Windows will clear out 15M of memory that hasn’t been used in a while and

load the programload the program

Memory ManagementMemory Management The process of swapping memory in and The process of swapping memory in and

out creates the illusion that you have out creates the illusion that you have more than there really is (Virtual Memory)more than there really is (Virtual Memory)– Too much swapping is bad (poor performance)Too much swapping is bad (poor performance)– Windows hides the disk file from the userWindows hides the disk file from the user

Pagefile.sysPagefile.sys It is usually around 1.5 times the size of real It is usually around 1.5 times the size of real

memorymemory

Other uses of memoryOther uses of memory– Disk cacheDisk cache– RAM diskRAM disk– I/O buffersI/O buffers

Context Switching & Context Switching & MultitaskingMultitasking Context switching allows several application Context switching allows several application

programs to be in RAM at one time. The user programs to be in RAM at one time. The user controls which program is the current one.controls which program is the current one.– The user switches back and forth between programsThe user switches back and forth between programs

Multitasking allows several application Multitasking allows several application programs to be in RAM at one time. Each is programs to be in RAM at one time. Each is allowed CPU time as needed, all under the allowed CPU time as needed, all under the control of the CPU.control of the CPU.– Allows programs to continue to run in the back Allows programs to continue to run in the back

groundground

MS-DOS / Windows 3.1 / Windows XPMS-DOS / Windows 3.1 / Windows XP

OS for the Networked WorldOS for the Networked World Parallel processing / multiprocessing takes Parallel processing / multiprocessing takes

place on a computer with more than 1 CPUplace on a computer with more than 1 CPU– Requires more complex operating systemRequires more complex operating system– Utilizes special programming techniquesUtilizes special programming techniques

Distributed processing utilizes a network to Distributed processing utilizes a network to decentralize and distribute the computing decentralize and distribute the computing needs over several dispersed computersneeds over several dispersed computers– SETI screen saverSETI screen saver

Client / server computing – the server Client / server computing – the server provides data and programs for the clientsprovides data and programs for the clients– Web server and web browsersWeb server and web browsers

OS for the Networked WorldOS for the Networked World Real Time processing – involves human Real Time processing – involves human

interaction with the computer in a situation in interaction with the computer in a situation in which quick or timely return of results is which quick or timely return of results is importantimportant– ATMATM– Airline reservation systemAirline reservation system

Process control – is the control of a process by a Process control – is the control of a process by a computer. It usually requires input to be computer. It usually requires input to be accepted by the CPU, processed, and then a task accepted by the CPU, processed, and then a task is executed based upon the processed input. is executed based upon the processed input. – Automobile electronic ignition systemAutomobile electronic ignition system– Missile guidance systemMissile guidance system– Usually require “feed back”Usually require “feed back”