Computer systems

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  • Computer systems
    • Systems
      • A system is a collection of parts that work together for a common purpose
        • For a system to be useful, it must produce something - an output
          • It needs to receive and process inputs in order to produce outputs
        • Systems often interact with other systems
        • Systems may be made from many sub-systems
          • Interconnections between systems are called interfaces
        • A computer system is a system that is able to take a set off inputs, process them and create a set of outputs
          • This is done by a combination of hardware and software
      • Most electric and electronic devices rely on computer systems
        • For example, a car has over 50 processors that control most of its functions
          • Instead of lots of power cables, control signals are passed along a bus to the actuator which carries out the job such as raising the window
        • Most computer systems in electronic devices are dedicated, which means that they are designed specifically for that one job
          • They are called embedded systems because they are part of another device
          • Other computer systems are general purpose, meaning they can be used for different reasons according to what work needs to be done
            • PCs are general purpose, and can run word processors, browse the internet, and play music and movies
      • The kernel is the lowest level of an operating system that controls the hardware
    • Importance
      • Computer systems are involved in most human activities
        • Safety - guiding aircraft, controlling trains, supporting signalling systems, monitoring patient body signs
        • Travel - smart phone apps, GPS systems, train timetables, flight bookings
        • Business - orders, stock control, payroll
        • Retail - online ordering, logistics systems that control delivery of goods
        • Entertainment - DVDs, Blu Ray, MP3 players
        • Communication - email, chat, social networks, business transactions, mobile phones
        • Education - Virtual Learning Environments, exam marking, unlimited sources of information on the web
        • Politics and government - campaigns, voting (in some countries), payment of taxes
        • Science - number crunching, simulations, visualisations
    • Reliability
      • As we have become more dependent on computer systems, we need to be able to trust their reliabilty
      • Computer systems are so reliable that we don't give them much thought, but they can sometimes let us down
      • Unreliable computer systems can cause very serious problems
        • Aeroplanes rely on computer systems, so obviously any problems with these could be lethal
          • It is vital that the human operators understand what the computer systems are meant to do
        • They can result in the loss or theft of data
          • This type of problem is often related to poor procedures or non-compliance with procedures rather than computer system faults
    • Standards
      • Standards refer to conventions and rules
        • They are normally defined by a responsible organisation
      • In computing, standards exist for programming languages, operating systems, data formats, communications protocols and electrical interfaces
      • There are various categories of standards
        • Proprietary standards
          • These are standards owned by an organisation
          • They ensure compatibility between the company's products
          • They can be used to exclude others from competing with rival products
            • For example, Apple computers lock users into using Apple software
        • Open standards
          • These are publicly available standards that are often agreed by a group of collaborators and are not for profit
          • Examples include HTTP, HTML, WAP, TCP/IP, XML and SQL
        • Industry standards
          • These are set by industry-wide organisations
          • Many of these relate to hardware and allow easy interconnection between devices, e.g. USB
        • De facto
          • These have developed from common usage
          • Includes standards such as postscript, the QWERTY keyboard and the Microsoft Word file standard
          • These standards lack formal approval and are not recognised by any official standards organisations
        • De jure
          • This means 'by law'
          • They are de facto standards that have become so universally accepted that they have to be adhered to in order for devices and software to be able to communicate
          • Examples include wireless 801.11, TCP/IP, ASCII and Unicode
      • Standards are important because they:
        • Enable equipment from different manufacturers to work together
        • Make learning new systems easier
        • Minimise waste
        • Help to ensure fair play and access to markets
        • Bring costs down by opening markets to competition
    • Ethical, environmental and legal considerations
      • Ethical considerations are about what is morally right and wrong
        • It comes down to what people or society believe is right or wrong
        • These things are not illegal in themselves, but many people have very strong beliefs about whether they are right or wrong
      • Environmental considerations are about what is good or bad for the environment
        • The components that are used to make hardware devices usually contain plastics which are derived from oil, and metals which are very harmful to the environment
          • To encourage recycling, there is an EU directive called WEEE - Waste Electrical and Electronic Equipment
            • It places an obligation on an organisation such as schools and hospitals to dispose of old equipment by recycling
              • Therefore many companies now use recycling specialists to take away the old equipment and extract as much valuable material from it as possible, with the remainder going into landfill
              • Another option is to be in partnership with refurbishment specialists
                • They refurbish old computers that still work, then sell them on or donate them to worthy causes
                  • This has two benefits:
                    • People who can't afford the latest computers can now use older ones
                    • Computers stay useful for longer, avoiding landfill or recycling for a while longer
        • Computer systems use up a lot of electricity to run and keep cool
          • So manufacturers now design equipment that uses as little energy as possible
            • Sleep mode effectively shuts down the computer if it hasn't been used for a while
            • Real, physical servers are now so powerful that they spend much of their time doing nothing, because they get the jobs requested of them done in nanoseconds
              • This low load is very inefficient - it wastes energy and money
                • A virtual server is an 'image' of a complete server that runs as a software program on the physical server
                  • Many virtual servers can now run on one physical machine, so the loading is much higher
                    • This means it's more energy efficient
      • Legal considerations are about what is legal or illegal according to the law of the country
        • The Computer Misuse Act makes it illegal to gain unauthorised access to computer systems (hacking)
          • It also makes it illegal to deliberately damage another person's computer system, for example by introducing a virus in it
        • The Data Protection Act gives clear guidelines on how organisations should obtain and process people's personal data
          • It demands that those who keep personal data on computer systems should take care of it and protect it from unauthorised people

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