Master Boot Record - external to partitions.
  Master Partition Table - parameters for the primary partitions on drive.
    Limited to 4 entries on Intel systems.

  Master Boot Code - Initial code after BIOS boot strap.

Master boot record describes partitioning :

Partitioning
  4 "Primary" partitions (Dos compatible).
 
  1 of these 4 marked as active (working OS location)
    Note each of the 4 can have an OS and active flag can be moved. 
 
  DOS must be on a primary partition.

  Other OSes, including XP, may not have this restriction.

  One of the primary partitions can be flaged as extended.
    Some OSes recognize one extended partition and one primary at a time.

    Some OSes can recognize more but may be problematic
 
  Each partition has a volume boot record describing particular partition.
    Disk Parameter Block - size, # of sectors, label name, cluster size, etc. 
      A particular partition has specific single settings 
      but different partitions can vary one from another.

    Volume Boot Code - called by Master Boot Code if active partition.

  Extended partition can further be parsed up into logical partitions.
    For dos, up to 23 labeled as D-Z 

    On booting, volume boot record used to sequentially link and recognize 
    each logical drive. 

Partitioning provides for a way around the size limits of the DOS FAT.

Patition Comparison
   
Usage.
  Separate OS, swap area, user data.

  Allow a large drive to be partitioned into smaller virtual drives.
    Smaller clusters, closer match to chs limits.

  Multiple OSes on same system.

  Recovery partition/software on disk.