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Introduction to Computers. What is an OS (operating system)?. Master controller of all tasks on a computer Manages the sharing of computer resources A resource is any component required to do work Programs contend for computer resources
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What is an OS (operating system)? • Master controller of all tasks on a computer • Manages the sharing of computer resources • A resource is any component required to do work • Programs contend for computer resources • Increases productivity by setting a consistent and easy user interface to accomplish tasks • Provides a platform for application software • Supplies utilities to address needs common to most applications such as printing
managing resources • Consider a home with 1 shower & many people • There is contention for the shower in the morning • What determines the order in which occupants are allocated the shower resource? • A locked door prevents Jimmy from using the shower at the same time as Susie • The locked door implements a first-in, first-out (FIFO) allocation system • Computers use a similar scheme to allocate scarce resources
Managing Processor resources • The processor executes many tasks at once • OS must insure all tasks get processing time • OS switches from task to task, typically when a process will take an extended period of time • Opening a disk file takes a second or two • Processor issues command to open the disk file • Then switches to another task while file is opened • This maximizes processor efficiency • All tasks seem to happen simultaneously
Managing memory resources • Each program gets a portion of RAM • Includes each application & the OS as well • OS keeps instructions & data of one program from “leaking” into RAM allocated to another • If OS fails to do this, program will “crash” • What if Word Data uses portion of RAM allocated to the Excel Program? • Word Data writes over the Excel program instructions • With instructions missing, the program fails
managing storage resources • Acts as a filing clerk • Keeps track of name and location of every file • Keeps track of empty space for new files • Uses FIFO system to fulfill storage requests • Takes each read or write request one at a time • Next request processed only after current one filled • Insures data for 2 distinct tasks not mixed together
managing peripheral devices • OS must know characteristics of peripherals • Recognizes and configures each different device • Insures each device is functioning correctly • Must format data as needed for that device • FIFO scheduling required for a network printer • Two users submit a print job at the same time • Don’t get a page from one job, then from the other • This would be an awful mess to sort out • Instead, first job submitted is printed in it’s entirety
OS sets the user interface standard • User interface is the means used to direct the activities of the computer • Windows uses a keyboard, mouse, & icons you click to create a graphical user interface (GUI) • DOS used a keyboard to type commands, referred to as a command-line interface • OS dictates what the user sees and how tasks are initiated • Application software usually follows the standard set by the operating system
User interface examples • The look and feel of two different user interfaces can be vastly different • A graphical user interfaceA command-line interface
GUI versus command-line interface • Each have their strengths • The GUI interface: • Requires far greater software complexity • Requires far more computer resources • But is much easier for novice users • The command-line interface • Greatly simplifies the operating system • Places few demands on computer resources • But requires more knowledgeable users
Provides platform for applications • Printing is a common application software need • The OS handles the details of the printer interface • Relieves each application from the details of working directly with the printers • Instead, applications just “hand off” a print job to the operating system, which does the rest • Each application developer doesn’t have to “re-invent the wheel”
Popular PC operating systems • Windows 7, Windows 8, and Windows 10 • Used with Intel/AMD X86 processor family • Often referred to as the Wintel platform • Uses a GUI interface • Linux • Also used with the Intel/AMD X86 processor family • Uses a command-line interface • Mac OS • Provides a GUI interface for the Macintosh platform
The windows operating system • The dominant personal computer OS • But not mobile devices which use Android or iOS • There have been many versions of Windows • Windows 3.1 ran as an application program using the DOS (Disk Operating System) • Since then, Windows versions have been a true OS including 95, 98, ME, XP, Vista, 7, & 8 • Current version is Windows/10 • Many now moving from Windows 7 or 8 to Win/10
Windows versus Linux • Most operating systems are proprietary • Meaning they are owned by a person or company • Must pay a license fee to use a proprietary operating system • Computer makers license Windows for each new computer they sell • Cost of Windows is buried in cost of a new computer • Linux is a free operating system • Open source, allowing users to customize the OS • Distributed free under a General Public License
Linux is gaining in popularity • Free is a major attraction • But it’s unlikely Linux will supplant Windows • Uses a command-line interface so must be more technically savvy to use it • Not nearly as pre-packaged as Windows software • Installing and configuring software can be trying • Far less application software available for Linux • Support is non-existent unless willing to pay companies such as Red Hat for support
Popular uses of Linux • Since Linux uses a command-line interface it requires far less hardware resources • Can be used to extend life of an outdated computer • Many web servers run Linux along with: • Apache as the web server software • PHP as a programming language • MySQL for a database • All are free, open-source software • Provides a very functional, low-cost web server
types of operating systems • Single-user OS designed for one user at a time • Personal computers have a single-user OS • Multi-user OS deals with many users at a time • Mainframe computers have a multi-user OS • Multi-tasking OS has memory management capability to run many programs at one time • Windows is a multi-tasking operating system • DOS was a single-tasking operating system
Loading the operating system • The operating system is always an active task and in RAM while the computer is running • The operating system is loaded into RAM and begins executing when the computer boots up • The boot up process at system startup: • Bootstrap program in ROM executes automatically • Bootstrap program tells the processor where to find the OS and how to load it • Bootstrap program transfers control to the OS once it’s been loaded
User has some interaction with OS • Most of what an OS does is behind the scenes • But users interact with it in the following ways: • Use the OS to start programs (the desktop) • Use the OS to manage files (Windows Explorer) • Customize the user interface (Control Panel) • Configure equipment (Plug and Play) • Search the OS for help info about various tasks