A computer system consists of ...

• the hardware,

• the software,

• the data,

• the people

... and the ways they all interact.

When a company needs a computerised solution to a problem, they call on a systems analyst to oversee the 

• analysis - finding out what's needed
• design - designing the new system
• development - creating the new system
• testing - making sure it works 
• implementation - getting it up and running

....of a new computer system....and possible...

• maintenance - updates, alterations and 'tweaking'.

More correctly....

........systems analysis involves a detailed study of an existing system and requirements of a new system...

........and systems design involves the design of the new system (hardware, software, data and people)

Businesses may need a new computer system because...

• they do not have one (they may only have a paper-based system)
• the one they are using no longer serves its purpose (the business may have changed or expanded)
• technological advances have made the current one obsolete
• competitors have better systems and are attracting more customers.