OPERATING SYSTEMS Software in the Background Chapter 2

Objectives Describe the functions of an Operating System Explain the basics of a personal computer operating system Describe the advantages of a graphical operating system Differentiate among different versions of Microsoft Windows Explain the need for network operating systems Describe the methods of resource allocation on large computers Be able to describe the differences among multiprocessing, multiprogramming, and timesharing Explain the principles of memory management List several functions typically performed by utility programs

Contents Operating System: Hidden Software Systems Software Functions of OS Types of OS MS-DOS Microsoft Windows Mac OS UNIX LINUX Network Operating System NOS Resource Allocation Utility Programs

Operating System Hidden Software Definition – provides access to all resources Kernel Manages the operating system Memory resident Loads set of programs that lies between applications software and the hardware Fundamental software that controls non-resident portions of the OS as needed Booting – Loads the kernel into memory

Systems Software Definition: Components All programs related to coordinating computer operations Components Operating System Utility programs Program language translators

Functions of OS Manage the computer’s resources CPU Memory Disk drives Printers Establish a user interface Execute and provide services for applications software Carries out all input and output operation

User Interface Facilitates communication between the user and the operating system Two forms Command line Text-based Key commands Examples: MS-DOS, Unix Graphical user interface (GUI) Visual images Menus Examples: Windows, Mac OS, Linux

Platform Definition: Wintel Computer hardware and operating system software that dictate what other software can run Wintel Intel-based PC running Microsoft Windows

OS is Hidden User interested in application software to make the PC useful Application software is platform specific User must be aware of the type of OS User should be aware of the functions of OS

Network Operating System (NOS) Types of OS Command line Single user PC Network Operating System (NOS)

MS-DOS Command-line interface Prompt – system is waiting for you to do something Key a command Not user-friendly

Microsoft Windows Graphical user interface Eases access to the OS Most new computers come with Windows already installed

GUI On-screen pictures Fast Easy Intuitive Icons Menus Pull down Pop up Click to activate a command or function Fast Easy Intuitive

Early Days of Windows Operating environment for MS-DOS Shell – layer added between users and DOS

Windows Today Home/consumer market Corporate market Windows XP Windows Millennium Edition (ME) Corporate market Windows NT Windows 2000 Windows XP Pocket computers and Internet appliances Windows CE

Windows 95 and 98 Self-contained OS DOS commands still available Start programs by Start button Double clicking the icon Task bar permits movement between open programs Long file names up to 255 characters Plug and play Object linking and embedding (OLE)

Windows 98 Additions Internet / intranet browsing Support for DVD and additional multimedia components Support for large hard drives TV viewer and broadcast ability Wizards

Improved Windows Features Backup Interfaces with other software Networking features Security Dr. Watson

Windows Helps reduce the cost of owning and maintaining a PC

Windows ME Millennium Edition Multimedia support -- Windows Media Player 7 Jukebox Record music CDs as digital files Windows Movie Maker Basic video editing Windows Image Acquisition Scanner and digital camera

Windows ME Millennium Edition Reliability Features System File Protection AutoUpdate System Restore Help Center Home Network Support Wizard for connecting multiple computers and peripherals Multiple users can share a single Internet connection

Windows NT New Technology Engineered for stability Strong security Versions NT Workstation NT Server Drawbacks Lacks support for older Windows and MS-DOS software and hardware Complex to learn and use Requires more memory and processing power

Windows 2000 Stability features Security features Uses simple approach to hardware setup from Windows 98 Versions Windows 2000 Professional for individual users Windows 2000 for network servers Was intended for both the corporate and home use, replacing Win NT and Win 98

Windows 2000 Complex Heavy demand for computer resources Improvements over windows NT Maintains user preferences Self-healing applications software Supports Windows 98 file structure Uses plug and play Provides improved support for laptops

Windows XP Extends Windows ME and provides a more stable environment Two categories Network server 3 versions based upon network complexity Desktop computer 2 versions Professional Client Personal Client

Windows CE Consumer Electronics Where used Embedded systems Industrial controllers Robots Office equipment Cameras Telephones Home entertainment devices Automobile navigation systems Pocket PC Internet appliance market

Windows CE Consumer Electronics Subset of Windows Less memory Smaller screens Little or no file storage Provides Internet connectivity

Accessibility Options Seeing Hearing Touching

Mac OS First commercially successful GUI (1984) Served as a model to other GUI systems

UNIX Supports Character-based system Command-line interface Multi-user Time-sharing Character-based system Command-line interface Runs on various processors and many types of computers Primary OS used on Internet servers

LINUX UNIX-like OS Open-source software PC Setup Download it free Make changes Distribute copies Restriction – any changes must be freely available to the public PC Setup PC comes with Windows installed Install LINUX in a dual-boot configuration

LINUX Advantages over Windows Disadvantage Extremely stable Internet support Reinstallation is simpler Disadvantage Scarcity of applications

Network Operating System NOS Designed to permit computers on a network to share resources Examples Windows 2000 Server Novell Net Ware Provides Data security Troubleshooting Administrative control

NOS Functions Split between client and server computers Server Client File management Client Requests to the server Messaging Has own local OS Makes the resources appear as if they are local to the client’s computer

Large Computers Used by many people at once OS works “behind the scenes” so users can share OS must control Who gets access to resources What keeps the programs from different users from getting mixed up with one another

Resource Allocation Resource – hardware or software that is needed to complete a task Resource Allocation – assigning computer resources to certain programs Resource De-allocation – releasing resources when a task is complete

Allocating the CPU One CPU More than one CPU Multiprogramming Event-driven Timesharing More than one CPU Multiprocessing – multiple CPUs can run several programs simultaneously

Multiprogramming One CPU Concurrent execution of two or more processes Several processes open at once Only one process can receive the attention of the CPU at any given moment Effective because CPU speeds are many times faster than input/output speeds

Event-driven Multiprogramming One program receives the attention of the CPU Its processing will be interrupted based upon events in the program When processing needs to be temporarily suspended, an interrupt is generated This is a signal to the operating system to evaluate the cause of the interrupt and determine who should now have CPU time

Event-driven Multiprogramming Example Two programs are running – Payroll and Inventory Management Payroll needs to read an employee record Payroll generates an interrupt Normal processing is temporarily suspended The CPU looks at the interrupt and initiates the read operation While waiting for the read to complete, the CPU begins processing the Inventory Management program

Event-driven Multiprogramming Example When the read operation is complete, another interrupt is generated Normal processing is temporarily suspended The CPU looks at the interrupt and determines its cause The CPU will either continue processing the Inventory Management program or return to the Payroll program depending upon their priority

Time-sharing Multiprogramming One program receives the attention of the CPU A small fraction of CPU time is allocated to the program The time slice ends The CPU begins processing a different program Response time can vary based upon the number of users on the system

Sharing Memory Program must be in memory to be executed Problems Programs compete for space May have a very large program Memory space for each program must not overlap

Memory Management The process of providing separate memory space to programs Memory Protection keeps one program from interfering with another

Memory Management Methods Partitions or regions Foreground and background Virtual storage (virtual memory)

Partitions or Regions Divide memory into sections The partition must accommodate the largest possible program Problem May cause wasted memory space

Foreground and Background Programs are placed in either Foreground or Background Programs in Foreground have priority for CPU time While performing read / write operations for the Foreground program, the CPU gives time to a program in Background Programs are placed in a holding queue while waiting to run

Virtual Storage Virtual Memory Uses concept of Paging Divide the program into equal-size pieces (pages) Store each piece in equal-size memory spaces (page frames) Typical size is 2KB or 4KB Create an index to each page and store in a Page Table

Virtual Storage Virtual Memory Paging Process A portion of the program is placed in memory The remainder is on disk Sections on disk will be brought into memory as needed (one page at a time)

Virtual Storage Virtual Memory Problem -- Thrashing Too large a portion of CPU time is spent locating the correct page and bringing it into memory Solution Run fewer programs concurrently Add memory

Memory Protection Keeps one program from straying into another Confines each program to certain defined limits in memory Why needed Possible for one program to destroy or modify another by transferring to the wrong memory location May cause destruction of data Action if assigned memory space is violated Termination of executing program

Sharing Storage Several users need to access the same disk pack One wants to write Another wants to read OS keeps track of the I/O requests OS processes I/O requests in order received

Sharing Printing Resources Print resources are shared between active programs Printouts are generated in pieces as the CPU gives each concurrent program some time Problem The current program may generate a few print lines The CPU moves to the next program The second program may generate a few print lines, etc.

Sharing Printing Resources Result Printout is worthless as it contains a few lines from several programs Solution – Spooling Each program thinks it is writing to the printer The program actually writes to the hard disk When the program is complete, the file on the hard disk is sent to the printer

Additional Printing Problem Printers are slow compared to the CPU speed Solution The CPU writing to the disk The program completes quicker

Utility Programs Come with System Software Handle special needs Perform secondary chores Do not need to be memory resident

Functions of Utility programs File manager – provide access to lists of stored files Backup and Restore – make duplicate copies of important files and return the copy to the hard drive if needed File compression – reduces the amount of disk space required by a file Disk defragmenter – reorganize files so they are stored contiguously on disk providing for faster access Device drivers – convert operating system instructions into commands that are known to a specific device