CS 1308 Computer Literacy and the Internet

Introduction  Von Neumann computer  “Naked machine”  Hardware without any helpful user-oriented features  Extremely difficult for a human to work with  An interface between the user and the hardware is needed to make a Von Neumann computer usable 2

System Software: The Virtual Machine  System software  Acts as an intermediary between users and hardware  Creates a virtual environment for the user that hides the actual computer architecture  Set of services and resources created by the system software and seen by the user 3

Figure 6.1 The Role of System Software 4

BIOS  Basic Input/Output System  The first piece of software that starts when the computer is turned on  Stored in Flash Memory  Power-on Self-test (POST) makes sure that all the system components are running properly (e.g. RAM check)  Gets the keyboard, mouse, and other peripherals started  Finds the “Boot” device and starts the operating system  For more information (Google “How does the BIOS work”) 5

Types of System Software  System software is a collection of many different programs  Operating system  Controls the overall operation of the computer  Communicates with the user  Determines what the user wants  Activates system programs, applications packages, or user programs to carry out user requests 6

Functions of an Operating System  Five most important responsibilities of the operating system  User interface management  Program scheduling and activation  Control of access to system and files  Efficient resource allocation  Deadlock detection and error detection 7

The User Interface Operating system Waits for a user command If command is legal, activates and schedules the appropriate software package Types of User interfaces Text-oriented – DOS, Unix, Linux Graphical – Mac, Windows, Linux Hybrid – Cell phones, digital cameras, PDAs Embedded –Microwave ovens, cars, etc. 8

System Security And Protection  The operating system must prevent  Unauthorized people from using the computer  User names and passwords  Legitimate users from accessing data or programs they are not authorized to access  Authorization lists 9

An OS provides security, e.g. against viruses ! 10 16M Shareware Game 0 Microsoft Word Doom DOS OS Memory the virus code Shareware Game Microsoft Word Doom DOS OS Memory When an “infected program” is run, the program counter (PC) might take the value of the first address of the virus code. Should this happen, the virus code will be executed. The virus code overwrites other programs in memory. How might the OS prevent this?

Efficient Allocation Of Resources The operating system ensures that Multiple tasks of the computer may be underway at one time Processor is constantly busy Keeps a “queue” of programs that are ready to run Whenever processor is idle, picks a job from the queue and assigns it to the processor Memory and secondary storage devices are used efficiently. 11

An OS Allocates Resources Efficiently:  It’s easy for an OS that supports a single user running a single program User tells OS to execute program 2. OS finds the program on disk 3. OS copies the program into memory 4. OS initializes the PC to the beginning of the program 5. Program monopolizes all computer resources bus disk memory CPU ALU PC registers Peripherals: monitors printers network connections etc. Doom Word Windows Netscape JAVA SPSS

This wastes computer resources  Input and Output are very slow  Disk and peripherals are 10,000x slower than the CPU  The user (typing on the keyboard) is even slower!  CPU time is wasted while waiting for them  During this time, CPU could be executing other programs! 13

Multitasking  Although it seems like your computer is running many programs at once, including the OS, it is not.  Your computer runs a bit of one program before switching to another.  And then switching again, often because it is waiting for I/O.  Because your computer is very fast, it seems like they are all running at the same time. 14

The Future Operating systems will continue to evolve Possible characteristics of fifth-generation systems Multimedia user interfaces Parallel processing systems Completely distributed computing environments – possibly over the internet (cloud computing) 15

Summary  System software acts as an intermediary between the users and the hardware  Your computer would be useless without an operating system and system software. 16