In the case of hard drives, these blocks are usually referred to as sectors . Reading data from or writing data to a hard drive is accomplished by specifying a particular sector number. The first is numbered zero, and the last is determined by the size of the hard drive. It's the operating system's job to impose some order on the hard drive sectors. The way the OS accomplishes this is by chopping a hard drive into pieces called partitions.
Most hard drives have just one partition, so users often confuse the two.
Partitions are also sometimes referred to as volumes. The operating system stores information about the paritions in the first several sectors on the disk. This area is known as the partition table. It records where each partition begins and ends and the type of volume format used for each partition. The volume format is determined by the file system used to access the information on the volume.