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Software Computer Systems Standard Grade Computing Studies


Title: Software Computer Systems Standard Grade Computing Studies Author: Perfect Papers Last modified by: ComptDept Created Date: 7/8/1998 7:17:27 AM – PowerPoint PPT presentation

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Title: Software Computer Systems Standard Grade Computing Studies

System Software Software The term that we use
for all the programs and data that we use with a
computer system. Two types of
software Program set of instructions that the
computer follows (e.g. a word processor or a
game). Data - what the programs process (e.g. a
word processing document or a saved game)
Programs There are two types of program
software. Systems Software Application
Software Systems Software Programs used to
organise the computer, handle its devices, manage
memory etc. The Operating System is Systems
Software. Applications software Programs
designed to carry out a particular task (Word
Processors, Databases, Graphics etc.)
  • Systems Software
  • A collection of programs than help the computer
    to work properly.
  • Includes
  • Operating System
  • Utility Programs
  • Translator Programs

Operating System Program that runs in a computer
from the moment it is switched on. After being
initially loaded into the computer by a boot
program, manages all the other programs in a
Standard Functions of the OS.
  • User interface
  • the OS provides the means of communicating with
    the computer system (Icons, commands etc. are all
    provided by the operating system).
  • Manages memory
  • The way that memory is allocated to programs is
    controlled by the OS.
  • Controls input/output
  • The access to all devices attached to the
    computer is controlled by the OS. For example,
    the OS can stop two programs trying to use the
    same device at the same time.

More OS - Standard Functions
  • The filing system manages backing storage
  • The access to all types of backing storage
    devices is controlled by a special part of the
    operating system called the filing system.
  • The filing system will prevent two programs
    trying to access the same files at the same time.

Resource allocation
  • When a computer is running the demands on the
    systems resources (i.e. memory, input/output
    devices, backing storage etc.) may be greater
    than the resources available. To deal with this
    a resource allocation system is built into the
  • Various techniques are used to prevent two
    programs demanding the same resource at the same
    time (e.g. two programs can't both send files to
    the printer at the same time).

The resource allocation system also ensures that
all programs running on the system receive as
much processing time as possible.
OS - Special Functions
  • Multi-programming
  • Also know as multi-tasking. Some operating
    systems allow more than one program to run on the
    system at the same time. This is possible
    because the resource allocation system shares the
    processors time between the different programs.
  • Multi-a ccess
  • Some operating systems allow many users to use
    the same computer system at the same time. Any
    computer system used in this way will have a
    multi-access operating system. The resource
    allocation system shares the resources of the
    computer system (discs, memory, processor etc.)
    between the different users.

OS - Different modes of processing
  • There are several different modes of processing.
  • Interactive
  • Accepting input from a human. Interactive
    computer systems are programs that allow users to
    enter data or commands. Most popular programs,
    such as word processors and spreadsheet
    applications, are interactive. In interactive
    processing, the application responds to commands
    as quickly as it can once they have been entered.
    Sometimes there is a delay while the processor
    finishes another task.
  • Real Time
  • Real-time operating systems are systems that
    respond to input immediately. Automatic teller
    machines for banks are an example of real time
    processing. Real time systems are used for tasks
    such as navigation, in which the computer must
    react to a steady flow of new information without

OS - Different modes of processing (cont.)
  • Executing a series of jobs (programs data) all
    at one time. The term originated in the days when
    users entered programs on punch cards. They would
    give a batch of these programmed cards to the
    system operator, who would feed them into the
  • Usually, batch jobs are stored up during working
    hours and then executed during the evening or
    whenever the computer is idle. Batch processing
    is particularly useful for operations that
    require the computer or a peripheral device for
    an extended period of time. Once a batch job
    begins, it continues until it is done or until an
    error occurs. Note that batch processing implies
    that there is no interaction with the user while
    the program is being executed.

OS - Different modes of processing (cont.)
  • Interactive systems with background job
  • Some operating systems allow a background process
    to occur at the same time as a foreground
    interactive process.
  • The foreground process is the one that accepts
    input from the keyboard, mouse, or other input
    device. Background processes cannot accept
    interactive input from a user, but they can
    access data stored on a disk and write data to
    the video display unit.

For example, some word processors print files in
the background, enabling you to continue editing
while files are being printed.
The Filing System
  • The system that an operating system uses to
    organise and keep track of files.
  • Catalogue/Directory
  • The filing system can access the contents of
    floppy and hard discs. The contents of these
    discs is held in the directory(also called
    catalogue). The filing system reads this
    information so that it can find any file on the
    disc straight away.
  • Types of File
  • Software can be stored on backing storage as
    files. There are two types of files.
  • Program files (such as the operating system, word
    processors etc).
  • Data files (such as graphics images, documents

Types of filing system
  • Flat filing system
  • All the files are organised into one large area.

  • Hierarchical filing system
  • A filing system in which directories have files
    and subdirectories beneath them.
  • A hierarchical filing system is one that uses
    directories to organise files into a tree

A Hierarchical Filing Structure
Types of access
  • Sequential Access
  • To go from file A to file Z in a
    sequential-access system, you must pass through
    all intervening files.
  • Sequential access is sometimes called serial
  • Random Access
  • Refers to the ability to access data at random.
    In a random-access system, you can jump directly
    to file Z. Disks are random access media, whereas
    tapes are sequential access media.

Systems Software
  • The operating system is just one example of
    systems software.
  • Other examples of systems software are
  • Anti-virus tools
  • Disk utilities
  • Programming tools
  • Printer manager utilities
  • All these are examples of programs. Programs can
    be written in a number of different ways...

Low Level Languages
  • Computers only understand binary!!!
  • All programs have to end up in binary language in
    order work.
  • The binary language that the computer understands
    is called MACHINE CODE
  • Machine code looks like this
  • 00100111,01110100,10010001
  • NOT very easy to understand.
  • Thats why High Level Languages and Assembly
    Language have been produced...

High Level Languages
  • We use high level languages (HLLs) because
    programming in low level languages like machine
    code is VERY difficult.
  • High level languages make it easier for us to
    write programs because we can use commands that
    mean something (PRINT, END, IF, THEN).
  • High level language programs still have to be
    converted into machine code to work. This is
    done by a translator.
  • There are lots of different HLLs but they all
    still have several things in common...

Common features of High Level Languages
  • English like words and phrases as instructions
  • Arithmetic operations such as multiply, divide,
    add subtract etc.
  • High level languages are problem orientated. This
    means that the programmer can forget about the
    internal workings and set-up of the computer
    system and can concentrate on solving the problem.

Common features of High Level Languages
  • Words and symbols are combined to conform to a
    predefined SYNTAX to produce program instructions
    (also called statements). Syntax are the rules
    which govern how the program commands are used
    (similar to the rules of grammar that govern how
    we use the English language).
  • Must be translated into machine code. A special
    program (a type of systems software) called a
    translator does this.

Types of translator
  • There are two types of translator for high level
  • Compiler
  • A program that translates source code into
    machine code. The compiler gets its name from the
    way it works, looking at all of the source code
    and collecting, reorganising and converting the
    instructions into machine code.
  • Compilers require some time to create an
    executable program. However, programs produced by
    compilers run much faster than the same programs
    executed by an interpreter.
  • The program produced by the compiler is
    executable. It does not need the compiler or the
    source code.
  • Many compilers are available for the same
    language. For example, there is a FORTRAN
    compiler for PCs and another for Apple Macintosh
    computers. This makes the program source code
    PORTABLE (able to run on a number of different
    computer processors).

Types of translator
  • Interpreter
  • An interpreter translates high-level instructions
    into a machine code line by line. Each HLL
    statement is converted, in turn, into machine
    code and then executed.
  • An interpreter can immediately execute high-level
    programs (unlike a compiler). For this reason,
    interpreters are sometimes used during the
    development of a program, when a programmer wants
    to add small sections at a time and test them
    quickly. Also interpreters are often used in
    education because they allow students to program
  • The advantage of an interpreter over a compiler
    is that it does not need to go through the
    compilation stage during which machine code
    instructions are generated.
  • Many interpreters are available for the same
    language. For example, there is a BASIC
    interpreter for PCs and another for Apple
    Macintosh computers. This makes the program
    source code PORTABLE.

Assembly Language
  • Machine code consists entirely of numbers and is
    almost impossible for humans to read and write.
    Assembly language has the same structure and set
    of commands as machine code, but it allows a
    programmer to use names instead of numbers.
  • Each type of processor has its own machine code,
    so an assembly language program written for one
    type of processor won't run on another.
  • In the early days of programming, all programs
    were written in assembly language. Now, most
    programs are written in a high-level language
    such as FORTRAN or C. Programmers still use
    assembly language when speed is essential or when
    they need to perform an operation that isn't
    possible in a high-level language.

Types of translator
  • There is one type of translator for assembly
    language programs.
  • Assembler
  • A program that translates programs from assembly
    language to machine language.

LDA 28 PRN 76 CLE 1 JMP 8
011000011100 101001001100 100100000001 11010000100
Types of High Level Language
  • General purpose
  • General purpose high level languages are written
    for a wide variety of tasks. They can be used
    for any type of application however they may lack
    certain commands that make particular tasks easy
    to do.
  • Special Purpose
  • Special purpose high level languages are written
    for particular types of task. For example Delphi
    is written for windows database programming and
    has special commands that make this type of task
    easier to carry out.