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CSCI-235 Micro-Computer in Science System Software System Software System software includes all of the programs needed to keep a computer and its peripheral devices running smoothly Two major categories of system software are: Operating systems System utilities © Prentice-Hall, Inc The Operating System The operating system (OS) is a set of programs that perform certain basic functions with a specific type of hardware The functions of the OS are: Starting the computer Managing programs Managing memory Handling messages from input and output devices Enabling user interaction with the computer © Prentice-Hall, Inc The Operating System OS stays behind the scenes All software depends on the OS Sales Summary Income Statement Office Inventory CAD GUI Operating System Tax Planning Human Resource Mgt. Loan Computer Evaluation Games System Investment System © Prentice-Hall, Inc Operating Systems for Large Computers Resource Assigning computer resources to certain programs and processes for their use Main allocation issues related to resource allocation Sharing the Central Processing Unit (CPU) Sharing memory Sharing storage resources Sharing printing resources © Prentice-Hall, Inc Sharing the CPU Multiprocessing Multiprogramming Time-Sharing © Prentice-Hall, Inc Multiprocessing The use of a powerful computer with multiple CPUs Multiple programs run simultaneously Each runs on its own processor © Prentice-Hall, Inc Multiprogramming Two or more programs executed concurrently Programs take turns using the CPU Event-driven • An interrupt suspends processing to allow another program to run • After the second program runs, the OS returns the CPU to another program © Prentice-Hall, Inc Time-Sharing Programs take turns using the CPU Time-driven Each user is given a slice of time (fraction of a second) CPU works only on that user’s tasks during his/her time slice Typically used in applications with many users © Prentice-Hall, Inc Starting the Computer – The process of loading or reloading the OS into the computer’s memory Booting © Prentice-Hall, Inc Starting the Computer The computer copies the kernel from the hard drive into the computer’s memory The kernel • • • • • Is the central part of the OS Starts all applications Manages devices and memory Resides in memory at all times Performs other essential functions © Prentice-Hall, Inc Managing Programs Single-tasking systems run one application program at a time Multitasking OSs have the ability to run more than one application program at a time Multitasking is accomplished by A foreground application • The active program or program in use One or more background applications • Inactive program(s) or program(s) not in use © Prentice-Hall, Inc Example of Multitasking Background application Foreground application © Prentice-Hall, Inc Storage Structure Programs must be in main memory (RAM) to execute Von-Neumann architecture Load instruction from memory into instruction register Operands fetched from memory to internal registers START Fetch next instruction from Memory to IR Increment PC Decode and Execute Instruction in IR NO STOP ? YES Storage Structure Ideally, we want programs and data to reside in main memory permanently Main memory is usually too small Main memory is volatile – loses contents on power loss Secondary storage holds large quantities of data, permanently Magnetic disk is the most common secondary-storage device Actually, a hierarchy of storage varying by speed, cost, size and volatility © Prentice-Hall, Inc Storage-Device Hierarchy Storage Technology Static RAM (SRAM) Dynamic RAM (DRAM) 50ns – 70ns, $20 – $75 per GB Magnetic disk 0.5ns – 2.5ns, $2000 – $5000 per GB 5ms – 20ms, $0.20 – $2 per GB Ideal memory Access time of SRAM Capacity and cost/GB of disk Managing Memory The operating system allocates memory areas for each running program; it keeps programs from interfering with each other The operating system uses virtual memory as an extension of random access memory (RAM) © Prentice-Hall, Inc Managing Virtual Memory hard disk page swapped in most recently transferred data or program instructions memory Virtual memory management swap file © Prentice-Hall, Inc page swapped out least recently used data or program instructions Virtual Memory and Cache Cache/VM: Analogy You are going to do some research on a particular topic. Thus, you go to the library and look for the a shelve that contains books on that particular topic You pick up a book from the shelve, find a chair, seat and start reading © Prentice-Hall, Inc Cache/VM: Analogy You find a reference to another book on the same topic that you are also interested in reading. Thus, you stand up, go to the same shelve, leave the first book and pick up the other book Then, you go back to the chair and start reading the second book Later on you realize that you want to read the first book once again (or another related book). Thus, you repeat the same process (i.e., go to the shelve to find it) © Prentice-Hall, Inc Cache/VM: Analogy Suppose that instead of taking just one book from the shelve, you take 10 books on the same topic. Then, you find a table with a chair, put the 10 books on the table, sit there and start reading one of the books If you need another related book, there is a good chance that it is on your table so you don’t have to go to the shelve to get it. Also, you can leave the first book on the table and there is a good chance that you will be needing it again later © Prentice-Hall, Inc Handling Input and Output Input and output devices generate interrupts, or signals, that tell the operating system that something has happened The OS provides interrupt handlers or miniprograms that begin when an interrupt occurs © Prentice-Hall, Inc Providing the User Interface The user interface is that part of the OS with which the user interacts with a computer © Prentice-Hall, Inc Types of User Interfaces Graphical user interface (GUI) Menu-driven Uses graphics to create a desktop environment Icons (small pictures) represent computer resources Programs run within on-screen windows Text-based menus are used to show all of the options available to the user Command-line The user is required to type keywords or commands in order to enter data or give instructions © Prentice-Hall, Inc Graphical User Interface (GUI) © Prentice-Hall, Inc Menu-driven User Interface © Prentice-Hall, Inc Command-Line Interface © Prentice-Hall, Inc Popular Operating Systems MAC OS WINDOWS XP UNIX MS-DOS © Prentice-Hall, Inc LINUX Microsoft Windows Click to view each Windows version (1985-2001) Windows Windows Windows Windows Windows Windows 3.x2000 ME NT XP 2.0 95 98 (1990-1992) 1.0(1998) (1995) (2001) (1993) (1987) (2000) (1985) (2000) © Prentice-Hall, Inc MAC OS Created in 1984 First OS to use graphical user interface Easiest operating system for beginners Mac OS X, was released in 2000 © Prentice-Hall, Inc MS-DOS Developed for IBM PCs in 1981 Uses command-line interface Use is diminishing © Prentice-Hall, Inc UNIX Developed by AT&T in 1970s Developed concepts of file management and path names Widely used by corporations © Prentice-Hall, Inc Developed in 1991 by UNIX Open-source code –Available for all to see and use More stable than Windows Powerful and free Growing acceptance © Prentice-Hall, Inc Linux System Utilities: Tools for Housekeeping System utilities are programs that help the operating system manage the computer system’s resources Types of utilities Backup software Antivirus software Disk scanning Disk defragmentation File management File-searching software File compression © Prentice-Hall, Inc Backup Software Backup software includes programs that enable the user to copy data from the hard disk to another storage medium © Prentice-Hall, Inc Antivirus Software Antivirus software protects the computer from computer viruses © Prentice-Hall, Inc File Management Utilities Known as a file manager Enables the user to perform various tasks on storage devices using files, folders, and directories © Prentice-Hall, Inc Tasks include: Creating folders Saving, deleting, copying, and moving files and folders Examining the contents of files Launching application programs Search Search programs enable users to find files on storage devices © Prentice-Hall, Inc File Compression Utility A file compression utility reduces the size of a file © Prentice-Hall, Inc Troubleshooting Computer Use a boot disk (emergency disk) in the floppy drive System startup failure slowdown Scan for viruses Defragment the hard disk © Prentice-Hall, Inc