Disk partition in dos, windows, linux, unix - 2

Compressed disks

Hard disks are sometimes compressed to create additional space. Under MS-DOS and early Microsoft Windows, programs such as STACKER (DR-DOS except 6), SuperStor (DR-DOS 6), DoubleSpace, or DriveSpace (Windows 95) were used. This compression was done by creating a very large file on the partition, then storing the disk's data in this file. At startup, device drivers opened this file and assigned it a separate letter. Frequently, to avoid confusion, the original partition and the compressed drive had their letters swapped, so that the compressed disk is C:, and the uncompressed area (often containing system files) is given a higher name. (SuperStor required a separate device driver to be loaded, DEVSWAP.COM).

Versions of Windows using the NT kernel, including the most recent versions, XP and Vista, contain intrinsic disk compression capability. The use of separate disk compression utilities has declined sharply.

Partitioning schemes

DOS, OS/2, and Windows

With DOS, OS/2, and Microsoft Windows, the standard partitioning scheme is to create a single active primary partition, the C: drive, where the operating system, utilities, applications, user data, and page/swap file all reside. Some users, however, prefer to create multiple partitions so that the operating system can be stored separately from other kinds of data. Proponents of multiple partitions generally point to the benefit of being able to erase a single partition (typically the operating system itself) while retaining the other data. When used in conjunction with third-party partition management programs such as Acronis Disk Director, Norton PartitionMagic, Norton Ghost, or specialized recovery programs that come with computers manufactured by most major manufacturers, the use of multiple partitions allows computer users to quickly recover from viruses, rootkits, and trojan horses or an otherwise damaged, corrupt or compromised operating system.

Windows Vista includes an inbuilt 'Disk Management' program which allows for the creation, deletion and movement of partitions.

Unix

For Unix-based and Unix-like operating systems such as Linux and Mac OS X, the creation of separate partitions for /boot, /home, /tmp, /usr, /var, /opt, swap and all remaining files under the "/" (root directory) is possible. (The same is true for Sun operating systems, except their partitions are called slices.) Such a scheme has a number of potential advantages: if one file system gets corrupted, the rest of the data (the other file systems) stay intact, minimizing data loss; partitions can be accessed read-only and the execution of setuid files disabled thus enhancing security; performance may be enhanced due to less disk head travel. This method has the disadvantage of subdividing the drive into fixed-size partitions, so a user could run out of hard drive space in his or her /home partition, even though other partitions still have plenty of usable space. A good implementation requires the user to predict how much space each partition will need, which may be a difficult task; especially for new users. Logical Volume Management, often used in servers, increases flexibility by allowing data in volumes to expand into separate physical disks (which can be added when needed); another option is to resize existing partitions when necessary. Typical desktop systems are often comprised of a single "/" (root directory) containing the entire filesystem plus a much smaller swap partition. By default, Mac OS X systems use a single "/" (root directory) containing the entire filesystem (including the swap file) as a point of simplicity (but other setup options do exist).

Partition recovery

When a partition is deleted, in general, only its partition table entry is removed from a table; and although the data is no longer accessible, it still remains on the disk until being overwritten. Specialized recovery utilities, (such as TestDisk and gpart), can locate lost file systems and recreate a partition table which includes entries for these recovered file systems. However, some disk utilities may also overwrite a number of beginning sectors of a partition they delete. For example, if Windows Disk Management (Windows 2000/XP, etc.) is used to delete a partition, it will overwrite the first sector (relative sector 0) of the partition before removing it. It may be possible to restore a FAT32 or NTFS partition if a backup boot sector is available.