Technical Disks-Formatting

Disks - Formatting

Formatting a disk requires logical and physical formatting. Physical formatting is sometimes known as low-level formatting and involves creating physical sectors on the disk, complete with address markings and then filling in the data portion of the sector with dummy data. New floppy disks are usually always physically formatted when you buy them, which wasn't the case several years ago. Logical formatting converts a disk to what is required of the operating system. When a disk is formatted with a style structure a kind of navigation is laid down for the operating system to use and make sense out of the disk.

The format command that is part of DOS or Windows does not physically format a hard disk, only a floppy disk. DOS does not include a command that physically formats a hard disk and no new hard disk should ever require low-level formatting. Certain types of controllers and drives will not allow you to perform a low level format yourself. If you attempt to low level-format there may be risk of using drive areas the manufacturer has identified as error prone or worse, hardware differences may uncover incompatibilities when attempting to do a low-level format. If you need to physically format a drive contact the manufacturer and obtain the proper software. SCSI drives are always pre-formatted for an operating system. Years ago many manufacturers would not honour warranties if a drive had been low-level formatted again. Taking a drive from an Apple Mac and using it in a PC required that you redo the low-level formatting for use with a PC which was expensive if the format failed and you had a useless warranty.

A floppy disk belongs to the operating system that formats it. Hard disks can be partitioned and used with more than one operating system. This is why DOS can not physically format your hard disk, only the floppy. DOS format uses a BIOS command to format the disk track by track. Before special features were added that keep an image of a disk all the data on an old disk was overwritten. Now, unless you specify otherwise an old disk is not physically overwritten with a hex value F6, between the time a disk is formatted and the time you try to unformat it.

DOS divides disks into two parts, a small system are that it uses to keep track of information about the disk and the data area. The system area is divided into three, the boot record, the FAT and the root directory. The boot record holds a small program that loads DOS into the computers memory, booting. The file allocation table (FAT) records the status of the disk which is broken into logical units called clusters. Data is stored in space assigned in the clusters. The size of the cluster varies from one disk format to another and can be as small as an individual sector. In addition the cluster size varies depending on the total size of the disk and the way the disk is designed. The root directory records the files that are stored on the disk. One entry for each file which records the name, the starting cluster number and the file attribute which records several things about the file. Every disk has a root directory and it is a fixed size for every disk format.
The data area records the contents of files on clusters which are all the same size on a disk. The record of which clusters and what order are kept in the disk's FAT. Files can be scattered in disjointed clusters after many reads and writes. When the files are scattered to much and fragmented things slow down as the hard disk moves the read / write head from sector to sector. Subdirectories are no different to a file as far as the way it is recorded on the disk but when it is used it acts like a disks root directory and holds a record of files and other subdirectories stored there. There is only one root directory on a disk but there can be many subdirectories and subdirectories can grow to any size the disk can handle. You have a fixed number of entries in the root directory whilst a subdirectory is only limited to the largest file the disk can support.

Upgrading A Computer

Memory Problems