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Disk Management in O/S

 DISK FORMATTING :-

  It is the configuring process of a data storage media sich as a hard drive, floppy disk or flash drive for initial use. Any existing file on the drive would be erased with disk formatting. Disk formatting os usually done before initial installation or before installation of a new O/S. It is also done if there is need of additional storage in the computer.
 
  A new magnatic disk is a blank state, it just a platter of magnatic recording material. Before a disk can store data, it must be divided into sectors that the disk controllr can read and write. This process is called low-level formatting or physical formatting. Low level formatting fills the disk with a special data structure for each sector . The data structure for each sector typically consistes of "a header, a data area and a trailer".

Header and trailer :-
  Header and trailercontain information used by disk controller, such as a sector number and error-correcting code (ECC).

Data area :-
  Most hard disks are low level formatted at the factory as a part of manufacturing process. For many hard disks,  when thye disk controller is instructed to low-level formate the disk, it can also be told how many bytes of data space to leave between all sectors. It is usually possible to choose among a few sizes, such as 256,512,1024 bytes.

Formatting a disk with a large sector size means that fewer sector can fit on each track, but it alo means that fewer header and trailers are written on each track and more space is available for user area. Some O/S can handle only a sector size of 512 bytes.

Before it can use a disk to hold files, the operating system still neds to record its own data structure on the disk. It does in two steps :-
 
i > Partition :- The first step is to partition the disk into one or more cylinders. The operating system can treat each partition as though it were a seperate disk. For instance, one partition can hold a copy of operating system executable code while another holds user files.

ii > Logical formatting :- The second step is logical formattung or creation of a file system. Data strusture omto the disk. These data structures may include maps of free and allocater space and an initial empty directory.


Cluster :-
   To increase efficiency, most file system group blocks together into large chumks, called clusters. Disk Input-output is done via blocks but file system Input-output is done by a cluster.

Raw disk :- 
    Some operating system give special programs, the ability to use a disk partition as a large block. The arary is of logical block. The array is sometimes called raw disk.
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