Hard Disk Parts and Fat
Storage Media Hard Disks DVD Disc
Optical Discs Tape Media Flash Drive
Zip Catridges RAID Removable Media
(U)niversal (B)us (S)erial        

Related Hard Disks Topics

How Hard Disk Works? Hard Disk Parts and FAT Hard Disk Myths MTBF of a Disk Drive
Password Security Lock S.M.A.R.T Upgrade Your Hard Disk Hard Disk Crash

Hard Drive Parts and FAT

by George Hernandez
Modified 2003/05/27
Here are the physical and logical parts of a hard drive.

A hard drive consists of a number of platters on a spindle.

  • The platters are read and written to with heads for reading, writing, and aligning.
  • Each platter has two sides.
  • Each side is divided into a number of rings called tracks. The tracks are numbered 0 on the outside and usually go up to 1023 track.

All the tracks on the platter form a cylinder. Cylinders are also usually numbered 0-1023.

Each track is divided into sectors. Sectors are the smallest chunk of bytes usable on a hard drive. Sectors are usually 512 B but are always to the power of two.

  • Contiguous tracks form clusters.

A hard disk has one MBR (Master Boot Record). A MBR holds the Partition Table which says how a disk is partitioned into up to 4 primary partitions, or 3 primary partitions and 1 extended partition

  • A primary partition has a specific file system (eg FAT or NTFS) and may even have system file for a specific OS (eg W95 or WNT). A primary partition is assigned a logical hard drive letter.
  • An extended partition is a contiguous portion of the hard drive that is not occupied by a primary partition. An extended partition is not formatted but it can be divided into multiple logical drives, each with its own letter, and those logical drives can be formatted.
  • Space outside of these partitions are wasted and are not considered free space.
  • If a drive does not need a primary partition than the whole thing can be an extended partition.
  • Free space within an extended partition on one or more disks can be combined to form a volume set, i.e. a logical drive with its own letter.

A computer may have multiple hard drives. When additional hard drives are added to a machine, the assignment of logical drive letters follows particular rules.

  • The 1st primary partition on the 1st drive always has drive C:.
  • The 1st drive will get the next letter(s) if it has additional primary partition(s).
  • The additional drive(s) will get the next letters before any logical drives in extended partitions on the 1st drive if they have primary partitions; other wise, any logical drives in extended partitions on the 1st drive get the next letters before any logical drives in extended partitions on the additional drive(s) get assigned a letter.

 Back to Top