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 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 RAM Operating System Word Program Word Data Excel Program Excel Data

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 interface A 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