computer science revision - 3
- Created by: lizzy.rawsthorne
- Created on: 03-06-17 19:14
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- software
- software is the term given to the programs that we run on our computers
- software also refers to the data that is used by the programs
- dedicated systems have software downloaded on a chip, this software is specific to the job and is only changed when updated.
- Multi-purpose computers such as laptops, tablet computers etc. regularly run different programs according to the desires of the user
- multi purpose computers store their software on a secondary storage medium such as:
- a hard disk, memory stick, SD card or optical disk
- multi purpose computers store their software on a secondary storage medium such as:
- system software controls the hardware
- application software handles the 'real-world' jobs that the user wants to do
- utility software has limited functionality and is used to maintain computer systems
- system software
- controls the hardware
- hides the complexities of the hardware from the user
- allows the user to operate the computer without having to write programs
- the main part of system software is the operating system
- user interface software
- an operating system must provide a way for a user to control and interact with a computer
- the user interface is the boundary between the human and user and the machine
- the interface: lets the user give commands, ask questions and displays a response
- graphical user interface (GUI)
- uses images, known as icons to represent resources, files, programs and actions.
- useful because they are: intuitive, no special training is needed, keyboard use is limited and no commands need to be learnt
- this interface sits on top of the operating system kernel and allows easy access to many of its everyday features, such as:
- selecting software, selecting files, sending messages
- natural language and speech
- some interfaces accept normal speech as input
- difficult to get right as speech can vary according to:
- accent, speed of talking, dialect, clarity
- difficult to get right as speech can vary according to:
- speech input can be useful for selecting options on telephone menus, giving commands to computers or dictating text.
- some interfaces accept normal speech as input
- memory management
- operating systems have to decide what goes where in memory, they have to make sure that:
- memory is used efficiently
- important data is not over written during the running of a program
- to do this, memory is divided into pages
- virtual memory
- sometimes there are more jobs than the memory can hold. the operating system then swaps jobs in and out of memory using a technique called virtual memory
- virtual memory means 'not real' memory
- a large program may take up too much memory so it is divided into modules
- the modules are stored separately on secondary storage
- when a module is needed it is loaded into memory and runs as a process
- when a different module is needed it can overwrite an unused module
- peripheral management
- a file is a named store of data on a secondary storage medium
- files can be:
- data files: such as a word processed document or a database
- program files: such as operating system components or applications
- configuration data: such as the parts of the windows registry
- files can be:
- a file is a named store of data on a secondary storage medium
- fragmentation and de - fragmentation
- secondary storage is divided into segments
- then files are split into blocks within these segments
- de - fragmentation is the process which tidies up the disk or other medium so that the parts of the files are moved to be stored next to each other
- secondary storage is divided into segments
- multitasking
- a multitasking operating system must:
- make sure that the CPU is in as much use as possible
- try to speed up the operation of all tasks
- share resources fairly between tasks
- when there are multiple processes running at the same time, the operating system uses a scheduler in order to allocate time.
- this allocation of time is made according to a policy
- for example:
- first come first served
- shortest job first
- all jobs get equal timing
- priorities
- for example:
- this allocation of time is made according to a policy
- a multitasking operating system must:
- operating systems have to decide what goes where in memory, they have to make sure that:
- programming software
- editors
- they allow text files to be:
- created
- saved
- read
- changed
- they allow text files to be:
- linkers
- these combine modules of object code into a single executable program
- interpreters
- convert typed commands into the machine instructions that the processor understands
- editors
- applications and utilities
- applications are the programs that people use to do 'real-world' jobs such as
- word processors
- traffic light controls
- games
- bar code readers
- utilities are software tools that help make maintaining the system easier
- for example
- antivirus software detect and remove viruses
- spyware protection
- firewalls monitor traffic entering and leaving a system
- for example
- system maintenance utilities help you clear away any redundant files
- system information and diagnosis utilities check fir problems on secondary storage
- system clean up tools search for un used files and clear them out
- automatic updating utilities check for online updates at intervals
- applications are the programs that people use to do 'real-world' jobs such as
- software procurement
- system managers must make choices so that their organisation gets systems:
- as required
- on time
- at a reasonable cost
- custom written software
- specially commissioned for a particular customer
- ADVANTAGES
- It should have the exact features required
- not require special adaptations to be made after installation.
- the developer can be contacted to solve issues
- the developer may provide training
- DIS ADVANTAGES
- may not have been extensively tested
- expensive
- long time to develop
- off the shelf software
- bought from supplier, ready to install
- examples include: Microsoft office, windows, Norton security software
- ADVANTAGES
- ready immediately
- extensively tested
- DIS ADVANTAGES
- probably not exactly what the customer needs
- search for trainers
- open source software
- placed in the public domain by the programmers
- examples: firefox, linux
- ADVANTAGES
- free of charge
- can be altered
- extremely reliable
- DIS ADVANTAGES
- no maintenance contracts
- no one to contact if there are any problems
- updates aren't regular
- proprietary software
- developed for a profit by a company
- ADVANTAGES
- someone to contact if there's any problems
- extensively tested
- updates regular
- DIS ADVANTAGES
- can be expensive
- deliberate in in compatibilities so users can be locked in
- inflexible to users needs
- system managers must make choices so that their organisation gets systems:
- software is the term given to the programs that we run on our computers
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