workflow task and work item?

Dear abapers,

i am posting this because i counldn't find any where in 'scn'.

as per the following link:

http://saptechnical.com/Tutorials/Workflow/WorkflowTutorialOne/WorkFlowTutorial1.htm

*******************************************************************************************************

The Tasks are the steps in the process, which have to be performed either by people or automatically by the software.

For example, to check for the availability of the spare computers in the company.

A Work item is the task instance that is performed as a single workflow step.

For example, check that there are no spare computers available in the company.

*******************************************************************************************************

what is the difference between task and work item?

as per above example checking availability of the spare computers in the company can be done by task, after finishing task's job it will return some message

about spare computers are there or not then why this work item,what is this work item?

about the above example i didn't understand anybody please elaborate clearly with another example about work item?