Computing and the Web Operating Systems

Overview n What is an Operating System n Booting the Computer n User Interfaces n Files and File Management n Input and Output of Information n Memory Limitations: Cache and Virtual Memory n Context Switching and Multitasking n Operating Systems for the Networked World

What is an Operating System? A collection of programs that manages and controls software, and coordinates the various hardware components to perform tasks requested by the user Isolate the hardware from users and direct manipulation by applications

What if the OS wasn’t there? n Programs “poked” into RAM via switches n First program loaded “read” other programs n Next program added “device support” n Devices could then be used to read in larger programs like BASIC n Overall process was tedious and slow (could take up to 30 minutes) n You wouldn’t want to shut off the computer

BIOS to the rescue n BIOS is the Basic Input Output System n Collection of programs n Provides the capability of communicating with peripheral devices –Keyboard –Disk drives –Monitor n Allows the rest of the operating system to be read in from the disk drive n Stored in ROM so it is always there

What is an Operating System? n A collection of programs that carry out six basic functions –Booting the Computer –Provides the User Interface –Provides File Management –Handles Input and Output Operations –Manages Memory –Provides Context Switching & Multitasking n Examples of Operating Systems: Windows (98, NT, ME, XP), MS-DOS, CPM, Mac OS X, UNIX, OS/2, LINUX, VMS, PALM OS, SOLARIS

Booting the Computer n Process of automatically running a program in ROM which in turn loads the operating system into RAM and turns control over to it. n Cold Boot – booting up when the power was originally off n Warm Boot – booting up when the power was originally on (re-booting) –Gets a fresh copy of the operating system n Multiple Operating Systems – partitioning the hard drive for each OS

User Interfaces n The user interface is the part of the Operating System that the user sees and interacts with n Different types of interfaces for different purposes –GUI –CLI n GUI – Graphical user interface –Mouse oriented and utilizes icons and buttons –Allows symbolic manipulation of programs and files n CLI – Command line interface –Instructions are given by typing commands on the keyboard –Requires technical understanding of commands –Not user friendly or intuitive

Files and File Management n A file is a collection of [data] that is treated as a single unit –A picture –A spread sheet –A document –A program n A file has a unique name –Filename. Extension n Extensions are used to associate files with programs

Files and File Management n There are two basic types of file systems –Flat file structure –Hierarchical file structure n Flat file structure –Organizes files in one flat list –No subdivision or grouping possible –Like dumping all of your papers in a pile on the top of your desk –Difficult to manage and keep track of files

Files and File Management n Hierarchical file structure –Organizes files in a tree like structure –Subdivision is achieved via subdirectories (usually depicted as folders) –Similar to filing cabinets with drawers and folders within them –Easy to manage and keep track of files –The folders become part of the naming convention for the file C:\Windows\System32\Regedit.exe

Input and Output Support n I/O support provides basic support to read and write information to peripheral devices n Specialized devices may require special software called a device driver –Device drivers are usually provided by the manufacturer of the specialized hardware –Device drivers provide enhanced features that the operating system doesn’t know about n I/O support also provides error handling in case of device failures

Memory Management n Real vs Virtual Memory n Computers have a physical amount of RAM n All memory in the computer is “owned” by the operating system n The operating system allocates memory to programs as they need it n The operating system reclaims memory when programs are done with it

Memory Management n Memory “some” PC after boot up

Memory Management n The user starts up a web browser

Memory Management n The user starts up several more programs

Memory Management The user wants to start a program that is 35M, but only 20M is free

Memory Management Windows will clear out 15M of memory that hasn’t been used in a while and load the program

Memory Management n The process of swapping memory in and out creates the illusion that you have more than there really is (Virtual Memory) –Too much swapping is bad (poor performance) –Windows hides the disk file from the user n Pagefile.sys n It is usually around 1.5 times the size of real memory n Other uses of memory –Disk cache –RAM disk –I/O buffers

Context Switching & Multitasking n Context switching allows several application programs to be in RAM at one time. The user controls which program is the current one. –The user switches back and forth between programs n Multitasking allows several application programs to be in RAM at one time. Each is allowed CPU time as needed, all under the control of the CPU. –Allows programs to continue to run in the back ground n MS-DOS / Windows 3.1 / Windows XP

OS for the Networked World n Parallel processing / multiprocessing takes place on a computer with more than 1 CPU –Requires more complex operating system –Utilizes special programming techniques n Distributed processing utilizes a network to decentralize and distribute the computing needs over several dispersed computers –SETI screen saver n Client / server computing – the server provides data and programs for the clients –Web server and web browsers

OS for the Networked World n Real Time processing – involves human interaction with the computer in a situation in which quick or timely return of results is important –ATM –Airline reservation system n Process control – is the control of a process by a computer. It usually requires input to be accepted by the CPU, processed, and then a task is executed based upon the processed input. –Automobile electronic ignition system –Missile guidance system –Usually require “feed back”