Transcript Introducing Large Scale Systems

Section 7
Introducing large scale systems
Section 7: Introducing
large scale systems
Introducing Large Scale Systems
AQA ICT A2 Level © Nelson Thornes 2009
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Section 7
Introducing large scale systems
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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Section 7
Introducing large scale systems
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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Section 7
Introducing large scale systems
Testing
Thorough testing
before the system
goes live should
keep problems to
a minimum.
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Section 7
Introducing large scale systems
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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Introducing large scale systems
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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Introducing large scale systems
Methods of introducing systems
Pilot changeover
The system is introduced on a limited scale, perhaps in a
single branch
The system is then rolled out to the rest of the organisation
Good opportunity to test under real conditions
Pilot system is available for training
Pilot may not find problems due to load on full system
Slower than direct changeover
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Section 7
Introducing large scale systems
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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Introducing large scale systems
Hardware installation
May include:
workstations plus peripherals such as printers
server (s), backup devices and uninterruptible power
supplies
network cabling or wireless access points
routers 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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Section 7
Introducing large scale systems
Software installation
May include:
applications software, loaded on workstations or
server
network and client operating systems
backup 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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Introducing large scale systems
Maintenance
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Introducing large scale systems
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
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