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AQA ICT A2 Level © Nelson Thornes 2009 Section 7 Introducing large scale systems 1 Section 7: Introducing large scale systems Introducing Large Scale Systems
AQA ICT A2 Level © Nelson Thornes 2009
Section 7Introducing large scale systems
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Section 7: Introducing large scale systems
Introducing Large Scale Systems
AQA ICT A2 Level © Nelson Thornes 2009
Section 7Introducing large scale systems
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Scale
Large scale systems will usually be mission critical – the organisation cannot function without them.
They will often involve more than one site and make heavy demands on infrastructure such as offices, equipment and networks.
There will usually be a need for a large number of staff to be trained.
The introduction must be planned in such a way that the organisation can continue to function during the changeover period.
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Scalability
Solutions based on generic software may not be feasible for large scale systems.
A database may work perfectly well with a few thousand records on a single server, but not with several million records across multiple sites on a wide area network.
Scalability may be difficult to test in practice and may need a simulated environment.
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Testing
Thorough testing before the system goes live should keep problems to a minimum.
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Methods of introducing systems
Direct Changeover
The existing system is stopped and the new one simply replaces it.
Quickest method, but highest risk.
Stressful, because old system is unavailable if problems arise.
System is down while data is transferred.
Training is difficult.
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Methods of introducing systems
Phased Changeover
System is brought in in stages, each stage replacing that stage in the old system.
Slower than direct changeover but less risky.
Each phase can be evaluated before moving on.
Hard to evaluate complete system until the end.
New system must be able to work with existing one.
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Methods of introducing systems
Pilot changeover
The system is introduced on a limited scale, perhaps in a single branchThe system is then rolled out to the rest of the organisationGood opportunity to test under real conditionsPilot system is available for trainingPilot may not find problems due to load on full systemSlower than direct changeover
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Methods of introducing systems
Parallel running
Old and new systems run side by side for a limited period
Safest method as both systems are available
Training is easier, but staff may become confused by using both systems
Very expensive and heavy load on staff and infrastructure
New system must be able to work with existing one
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Hardware installation
May include:
workstations plus peripherals such as printers
server (s), backup devices and uninterruptible power suppliesnetwork cabling or wireless access pointsrouters and switches.
The infrastructure must be designed to give all users access to the correct data at acceptable speeds and protect them as far as possible from data loss.
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Software installation
May include:
applications software, loaded on workstations or servernetwork and client operating systemsbackup software.
The network operating system controls and monitors security and must be configured to allow users correct levels of access.
Accounting can be set up to monitor or charge for system resources.
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Maintenance
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Bookshop
Imagine a small bookshop selling new and second hand books in a town popular with tourists.
How will its ICT requirements differ from those of a national chain of bookshops?
Think about: hardware software people procedures
