Disk Formatting

This article is made to answer our guest question when we discuss about What to Do If your Hard Drives Crashed.

Disk formatting is the process of preparing a hard disk or other storage medium for use, including setting up an empty file system.Large disks can be partitioned, divided into logical sections that are formatted with their own file systems. This is normally only done on hard disks because of the small sizes of other disk types, as well as compatibility issues.

There is two levels of disk formatting. There are low level formatting and high level formatting

LOW LEVEL FORMATTING

User instigated low-level formatting (LLF) of hard disks was common in the 1980s. Typically this involved setting up the MFM pattern on the disk, so that sectors of bytes could be successfully written to it. With the advent of RLL encoding, low-level formatting grew increasingly uncommon, and most modern hard disks are embedded systems, which are low-level formatted at the factory with the physical geometry dimensions and thus not subject to user intervention.

Early hard disks were quite similar to floppies, but low-level formatting was generally done by the BIOS rather than by the operating system. This process involved using the MS-DOS debug program to transfer control to a routine hidden at different addresses in different BIOSs.

Starting in the early 1990s, low-level formatting of hard drives became more complex as technology improved to:

* use RLL encoding,
* store a higher number of sectors on the longer outer tracks (traditionally, all tracks had the same number of sectors, as is still the case with floppy disks),
* encode track numbers into the disk surface to simplify hardware, and
* increase the mechanical speeds of the drive.

Rather than face ever-escalating difficulties with BIOS versioning, disk vendors started doing low-level formatting at the factory. Today, an end-user, in most cases, should never perform a low-level formatting of an IDE or ATA hard drive, and in fact it is often not possible to do so on modern hard drives outside of the factory.

HIGH LEVEL FORMATTING

High-level formatting is the process of setting up an empty file system on the disk, and installing a boot sector. This alone takes little time, and is sometimes referred to as a "quick format".

In addition, the entire disk may optionally be scanned for defects, which takes considerably longer, up to several hours on larger harddisks.

In the case of floppy disks, both high- and low-level formatting are customarily done in one pass by the software. In recent years, most floppies have shipped preformatted from the factory as DOS FAT12 floppies. It is possible to format them again to other formats, if necessary.