Computer Fundamental Materials-IT Students

1Partitioning a hard drive
When a new hard drive is installed it is completely blank. There are no spaces where files and folders can be stored. To create those spaces a hard drive must first be divided into logical sections. These sections are called partitions. The partitioning process creates spaces of contiguous sectors on the hard drive. Each partition can receive a file system for an operating system. Without a file system the partition is useless.
A hard disk can have up to four separate primary partitions, or three primary and one extended, or two primary and one extended, or just one primary and one extended partition on one hard drive depending on the user’s needs. DOS can have up to four separate partitions on any one hard disk. The extended partition uses the free hard disk space and is normally assigned all the available space outside the primary partition(s). DOS can only address a maximum of two gigabytes (GB) of hard disk space when using FAT16. FAT32 increases the limit to two terabyte (TB) of hard disk space. File Allocation Table (FAT) is discussed later in this module.
Note: Only the primary partition on any hard drive can be designated as active. DOS, Windows 95, and Windows 98 can only manage one primary partition per hard drive. Windows NT 2000 including some third party disk management utilities can be used to manage multiple primary partitions on a hard drive. A primary partition cannot be subdivided into smaller units.
Logical Drives
When a hard drive is partitioned the extended partition uses all the free hard disk space not included in the primary partition(s). There can be only one extended partition per disk. Unlike the primary partition it can be subdivided into a maximum of 23 sections called logical drives. Having multiple logical drives inside the extended partition provides some advantages:
• Rapid retrieval of information
• Multiple operating systems such as MS-DOS and Windows 98 can be installed on the same computer. However both drives must have the same file system or FAT.
• Logical drives physically separate information for organizational and security reasons.


By creating a second logical drive on the formatted hard disk, another complete file tracking structure is created on the hard drive. Frequently the operating system views this new structure on the hard drive as a completely new disk. Therefore a unique drive letter is assigned to it as mentioned previously.
FDISK, Boot Sector, and Partition Table
FDISK is the partitioning program for MS-DOS, Windows 9x, UNIX, and Linux. When partitioning a hard drive the FDISK program creates the disk boot sector. Typically the boot sector is the first area on each logical DOS disk or partition. When formatting the hard drive the information used to boot the operating system is recorded in the boot sector.

During the partitioning process FDISK also establishes partition information. On a drive that has been partitioned the partition information is in the form of a special table called the partition table. The partition table is located in the boot sector at the very beginning of the disk. Critical information is found in the partition table including the following:
• The location and starting point of each logical drive on the disk.
• Information on which partition is marked active.
• The location of the Master Boot Record (MBR). Only bootable disks have an MBR.
It is important that the partition table is at the beginning of the disk because this is where the system looks for boot up information.



Formatting a hard drive
After partitioning the drive it must be prepared to store data. This process is called formatting. Formatting a hard drive creates magnetic tracks in concentric circles on the disk surface. These tracks are then broken into chunks of 512 bytes called sectors. The tracks of the disk are numbered from the outer edge of the disk, inward beginning with 00 (zero zero). In the computer world numbering begins with 0 (zero) instead of 1. The number of tracks per disk depends on the type of disk and the drive in use. The combination of two or more sectors on a single track is called a cluster. A cluster is sometimes called a block. The size of each cluster depends on the size of the hard disk and the version of DOS in use.
A cluster is the minimum unit DOS will use to store a file. Even if a file is only one byte long, one whole cluster will still be used to store the file. The disk capacity is determined by the number of tracks and sectors and therefore, by the number of clusters that can be created on the disk surface by formatting it.
Note: Each sector on a DOS disk holds 512 bytes. Files can be any length and a single file may occupy several sectors on the disk. On floppy disks common cluster sizes are one or two sectors long. With hard disks the cluster size may vary from one to 16 sectors in length depending on the type of disk.
In a hard disk drive where several disks are stacked and rotate on a common spindle, all of the tracks having the same number are referred to collectively as a cylinder.