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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Geometry and Low-Level Data Structures | Hard Disk Formatting and Capacity ]

Two Formatting Steps

Many PC users don't realize that formatting a hard disk isn't done in a single step. In fact, three steps are involved:

  1. Low-Level Formatting: This is the "true" formatting process for the disk. It creates the physical structures (tracks, sectors, control information) on the hard disk. Normally, this step begins with the hard disk platters "clean", containing no information. It is discussed in more detail here.
  2. Partitioning: This process divides the disk into logical "pieces" that become different hard disk volumes (drive letters). This is an operating system function and is discussed in detail in its own section.
  3. High-Level Formatting: This final step is also an operating-system-level command. It defines the logical structures on the partition and places at the start of the disk any necessary operating system files. Read more about it here.

As you can see, two of the three steps are "formatting", and this dual use of the word is a big part of what leads to a lot of confusion when the term "formatting" is used. Another strange artifact of history is that the DOS "FORMAT" command behaves differently when it is used on a hard disk than when it is used on a floppy disk. Floppy disks have simple, standard geometry and cannot be partitioned, so the FORMAT command is programmed to automatically both low-level and high-level format a floppy disk, if necessary. For hard disks, however, FORMAT will only do a high-level format. Low-level formatting is performed by the controller for older drives, and at the factory for newer drives.

Next: Low-Level Formatting


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