FIFO - Once more

["Maureen J. Akins" <csvmja -at- ADMIN -dot- AC -dot- EDU>]

Okay - for all you non-computer scientists.  Here's the real info behind
FIFO.

FIFO means first-in-first-out.  (I don't know who originated it - the
accountants telling the computer folks or the computer folks telling the
accountants, but it is an accounting term also.)

In computer science terms, it is a method of processing information.  That
information can be stored in arrays, it can be stored in lists, or it can
be stored in any other data structure.  (If you aren't familiar with
these structures, read on.  You should be able to catch the rest.)  The
method of storing the information is important only so far as it supports
the method for processing it.  In the case of FIFO, you have to use a
structure that allows you to know which came first.

In general practice, the term 'queue' is often applied to FIFO processing.
Something is sent to the queue and the first thing sent to the queue is
processed first.  But, that order can be changed sometimes.  Printer
queues, for example, often have the capability of bumping something to the
front of the queue so that it prints next.  So while queues are often
FIFO processors, they don't have to be.

The term 'stack' means that information is stacked with the first thing in
being at the bottom and new information is added to the top.  You can only
get to whatever is on top - like plates in a cafetria.  There is no
way to reorder a stack, like there might be with a queue.  A stack is
always LIFO, last-in-first-out.

You should be careful when you use words like array or lists to describe
how data is stored within a program.  Programmers have a wide variety of
storage methods that they can use, depending on what they are trying to
accomplish.  A good programmer may even use more than one storage method
within the same program.  If you don't know for a fact that an array was
used at that point in the program, don't use the word array.

It is acceptable to discuss the order in which items are normally
processed.  So while you might talk about the printing being done on a FIFO
basis, you shouldn't say that the job information was stored in an array.

Hope this clears up the confusion about how FIFO, arrays, and stacks are
related.

Maureen

 -----
 Maureen Akins, Support Specialist
 Augusta College Computer Services,2500 Walton Way,Augusta GA 30904-2200
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