In computing, format is a command-line utility included in DOS, OS/2 and Microsoft Windows operating systems. The command is used to perform the following actions on magnetic media:
The boot record is placed in the location specified by the partition table. The FAT entries are cleared by changing them to 0x00.
The root directory is cleared out by changing any values found to 0x00. Format then checks each cluster to see if it is good or bad and marks it in the FAT. Unless you are using this command on a floppy disk and are using the /U switch, the data area is untouched. Data previously written to the media is still intact until it is overwritten when the cluster is reassigned to new data.
The format command must also be used in order to change a disk file system, as many operating systems will allow users to select the file system to format in.
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