[CS-FSLUG] Disk partitioning, difference between logical and primary partitions?

[N. Thompson]

I've always wondered what the difference between logical and primary 
partitions were, I've always used primary when partitioning but using that I 
can only fit so many partitions onto a disk before its full.

I was wondering what the difference between logical and primary partitions 
was, I think I remember seeing primary partitions nested in logical once 
before so I think logical partitions are for increasing a drive's capacity to 
store partitions. Am I correct?