For it to store and retrieve data on a hard drive, and keep track of multiple partitions and multiple drives, significant portions of OSs have to be dedicated to managing hard drives. A partition is a portion of a hard drive recognized by the OS as a separate and complete entity; it is not the divider between these portions as the name suggests.

File Systems

The OS has to have a method of storing and organizing files on a drive. There are different file systems used by Windows and DOS to serve that purpose:

File Allocation Table (FAT): Better known today as FAT16 for its 16-bit file storage, this is the original DOS and Windows file system. Its storage efficiency is the lowest of all file systems in use and it is highly susceptible to fragmentation (portions of files spread out all over the drive resulting in slow performance and additional wear). Additionally, FAT16 limits file names to eight characters plus a three-character extension. The maximum partition size for FAT16 is 4GB. FAT16 is the only file system accessible in all versions of Windows and DOS, and is the only file system usable by the original version of Windows 95 and older. It is also the file system for floppy disks.

FAT32: FAT32 stores files more efficiently than FAT16 and has support for long filenames. FAT32 drives can be read by every version of Windows since the second version of Windows 95 (except for NT 4.0), and is the default file system for 98 and Me. The maximum partition size for FAT32 is very large, although there is a 32GB limit in Windows XP.

NTFS: The original version of NTFS was introduced with Windows NT. A newer version was introduced in Windows 2000, and it is the default file system for 2000 and XP. NTFS is somewhat resistant to fragmentation and allows for many of Windows 2000 and XP's security features not available in FAT16 or 32. The maximum size for an NTFS partition is two terabytes (TB), which is 240 bytes, or 2048GB. Windows 9x and DOS cannot use NTFS.

To select a file system for a hard drive, you have to format the drive. When installing Windows 9x, you can use the DOS program FDISK, covered later in this tutorial. When installing 2000 or XP, the OS setup program provides this service. You'll be shown a graphical display of all the hard drives installed on the system, and you'll be given your choice for installation of the OS. You'll also have the choice of file systems, and NTFS will be recommended.

Partitions and Drive Letters

Here are definitions of the terms used in this area:

Active partition: This is the partition that needs to contain the OS's boot files because the BIOS looks to this partition for them. You can, however, designate any partition as the active partition; if it is the wrong one, the computer won't be able to boot from the hard drive.

Basic disk: A physical disk that is accessible by any version of Windows.

Dynamic disk: A disk used in 2000 or XP that can use special features such as logical disk volumes that span more than one physical disk.

Extended partition: A partition that can exist only on a drive containing the master boot record. An extended partition does not get a drive letter. To use an extended partition, you must create one or more logical drives on it; logical drives are assigned drive letters. There can be only one extended partition on a physical disk and you cannot install an OS on an extended partition. The only reason to create an extended partition is if you want to have more than four partitions on a physical hard drive.

Logical drive: A partition created on an extended partition. A logical drive can be assigned a drive letter.

Master boot record (MBR): The area on a hard disk that contains boot files; this is the first sector on the disk.

Physical disk: A hard drive.

Primary partition: A partition that functions as a physically separate disk. You can create up to four primary partitions on a physical disk that contains the MBR, or three if you create an extended partition also. Primary partitions normally are assigned a drive letter by the OS.

Volume: Any area on a hard drive that has a drive letter assigned to it.

The most important thing to know here is that you must designate a partition as active in order to boot from it. However, the other items are likely to come up at some time or another.

Drive Letters

In a PC, physical disks are designated a number starting from 0. Primary partitions, logical drives, optical drives, and network drives are assigned drive letters between C and Z (a network drive is a folder or drive on another computer on a network that can be accessed as if it were a local partition on the hard drive). A and B are reserved for floppy drives. The order of automatic letter assignment is as follows:

The first primary partition on drive 0 gets C.

Subsequent primary partitions on any drive get D, and so on.

Logical drives get the next available letters.

Optical drives get the next available letters.

Network drives get any available letters.

Note This lettering system can cause the following complications: suppose drive 0 has one primary and one extended partition with one logical drive. Drive 1 has one primary partition. Because primary partitions come first, the primary partition on drive 0 is C, the primary partition on drive 1 is D, and the logical drive on drive 0 is E. Furthermore, if you add a second hard drive to a system with a logical drive on drive 0, the new primary partition takes the drive letter formerly held by the logical drive.