UNIT OF STORAGE

data is stored in a pattern of concentric rings on a platter called tracks the tracks are further subdivided into sectors. OS's (like Windows) will group sectors together and call the grouping clusters.  There are lots of ways of accessing data on a drive. some use the native modes of the drive and can access a single sector if need be (look at data recovery programs or disk checking programs) and can even mark a sector bad and move it to a different part of the drive.  while other higher level access techniques will limit how the drive is accessed so that the minimum size is a cluster to allow for access.  So when you say "what will Windows allow" you have to specify how in Windows your accessing the drive to get a definitive answer.

WOULD IT BE A FILE, BECAUSE THAT IS ALL YOU CAN ACCESS FROM WINDOWS ABOUT THE HARD DRIVE?

That depends entirely upon what you mean by "access".  I took it to mean a standard read.  Your response indicates that you meant an open.  That's two different types of "access".  

Generally speaking...

A file access such as open operates at the file level.  A logical operation such as read or write operates on a cluster.  As jimmyd indicated, some programs operate on the track or even the sector, which is truely the very smallest access possible through standard operations.

So, it depends...

An "OPEN" does not really "access" the file it just sets up the I/O environment to be able to access the file. During the open process the allocation tables are being read to use the file. From windows there are many "things" about the drive you can access. properties only shows you the "drive" (# bytes). "Dir" shows you files, defrag shows you clusters. there are also tools that can show sectors.  So it all depends on what you are doing and what you want to accomplish.

Awesome homework question... you do know we aren't allowed to do your homework, right?

IT'S NOT HOMEWORK. I GOT STUMPED ON THE QUESTION ON THE TEST, WHICH I THINK I ANSWERED FILE. THE QUESTION TO ME WASN'T COMPLETELY CLEAR. I QUESTIONED YOU AFTER THE TEST.

So then why not say that in your question?  Why not explain what answer you think it is and we'll help you determine if you're right or wrong.

I BELIEVE CLUSTER WAS THE ANSWER THAT WAS SOUGHT