Software

Software

1. What is software?

   • Software: The programs that run on a computer
     • Application: Software designed to carry out a useful real world task
       • platform: A combination of hardware and operating system that supports the running of particular applications
         • programming language: A way of writing instructions for a computer to execute
   • Algorithm: Series of steps designed to solve a (mathematical) problem
     • Instructions: A set of commands that a processor can recognise and act upon
       • program: A stored set of instructions for a computer to execute
         • Known as software
           • run on hardware
       • loaded in RAM from secondary storage device
         • then fetched and executed by the CPU
         • e.g hard disk, memory stick, optical disk
   • utility software
     • limited functionality and used to maintain computer systems

2. System software

   • controls the hardware
     • without this programmers would have to take into account the precise movement of data between locations
   • hides the complexities of hardware from the user and application programmer
     • Allows user to operate the computer without writing all the programs
   • main part is the operating system
     • It's a set of programs that control the hardware
       • lets users and applications work with the computer
         • The Kernel enables the hardware to do things
           • looks after low level hardware operations
             • applications need this
               • to operate the hardware
         • Acts as an interface between the user and hardware
           • and betweeen applications and hardware
         • necessary to run all applications except self booting
           • ability of a program to load itself
     • transferes data between memory locations, the CPU and the disks
       • produces visual displays on the screen
         • protects data from being overwritten
     • known as a platform
   • includes:
     • interfaces
       • The boundary between systems or systems and humans
     • compliers
       • Translation software that converts high level source code to machine (object code)
     • interpreters
       • Translations software that converts source code or user inputinto machine code
     • linkers
       • software that combines together a number of separate object code files
     • debuggers
       • software that helps a programmer track down faults in the program
   • multitasking operating system
     • allows several processes to be resident in RAM at the same time
       • running, runnable or waiting
       • ensures programs are attended to the CPU as efficient as possible

3. Application software and utilities

   • handles real-world tasks for users
   • Use system software to make hardware do what is required
   • Utilities make maintaining the system easier.
     • e.g antivirus utilities and firewalls

4. security

   • operating systems must protect processes from each other
     • They must protect users from each other
     • If a process is using a certain part of RAM or storing data
       • another process must not be allowed to overwrite it
     • THe operating system divides memory into pages and keeps tabs
       • Where processes are using which pages to prevent conflicts
   • most systems are multi-user e.g networks all connected to servers
     • PCs are connected to the internet
       • so unauthorised users may gain access
   • operating systems keep track of who owns each process and file
     • They are marked according to privileges that've been granted
       • e.g read-write/read only
         • Only authorised users look but don't change anything
           • Set up on multi-user systems e.g Unix
             • At home firewall is set up
               • to take care of permission related security issues

5. files and directories

   • file systems
     • operating systems organise files on secondary storaage
       • files are stored in directories
         • directories can include subdirectories
   • A directory is a logical grouping of files
     • In windows they're called files
       • They make it easier for a human to locate related files
         • allow the use of the same file in different locations
   • File extensions are used in systems
     • part of the file name that indicates what files it is
   • attributes provide extra information e.g the creator

6. Writing software

   • programming language: A way of writing instructions for a computer to execute
   • CPU only recognises binary bit patterns
     • these instructions are known as machine code
       • MC Instructions in binary used by the CPU
         • machine code is a low level language
           • LLL- A programming language that is directed at controlling each machine operation
             • It work at the hardware level
       • machine code has to be written by a programmer
         • It is notoriously difficult
           • why there is attempts to make easier high level language
             • HLL- A programming language that resembles a natural language
               • each instruction translates to many machine instructions
                 • problem based not machine based
             • allow programmer to set out algorithms
   • software engineering: formal methods to guide the writing of software

7. software procurement

   • Custom written software
     • especially commissioned for a particular customer
     • Advantages
       • Have exactly features required
       • Not require special adaptions after installation
       • developer can be contacted to solve issues
     • Disadvantages
       • Not be tested completely
       • Expensive
       • Long time to develop
   • Off the shelf software
     • Bought from the supplier and ready to install
     • Advantages
       • Ready immediately
       • extensively tested
       • low cost
       • user reviews
     • Disadvantages
       • won't meet exact requirements
       • Have to search for training providers
   • Open source software
     • Placed on public domain by the programmers, produced to improve skills or public goof
     • Advantages
       • free of charge
       • Can be altered as source code available
       • Can be reliable and efficient
     • Disadvantages
       • no maintenance contracts
       • no contact if there's a problem
   • propriety software
     • Developed for profit by a company
       • only complied code is released, users buy a licence
     • Advantages
       • Someone who can solve a problem
       • extensivley tested
       • regular updates
     • Disadvantages
       • expensive
       • inflexible to users needs

8. user interface software

   • operating systems need to provide means of communicating with them
     • So the user can issue commands and allow applications to access their functionality
   • Command liine
     • Operating systems allow users to type in commands
       • allows customisation
         • commonly used commands are grouped together and run all at once
           • makes administering a network less effort
   • Graphical user interface
     • icons to represent resources and actions
       • reduce the need to learn commands
       • less customisable