active partition
A primary partition that is indicated in the partition table as the partition to use when loading the rest of the operating system. If a basic disk has multiple primary partitions, only one primary partition can be marked as active at a time. The primary partition's boot sector is used to load the rest of the operating system.
basic disk
An older, IBM-originated method used to organize disk space for x86 computers into primary, extended, and logical partitions. Basic disk technology is supported by many legacy operating systems and may be required in certain multiboot configurations.
boot partition
The partition or volume used to load the operating system from a hard disk. The system partition is processed before the boot partition. The boot partition can be the same partition as the system partition.
boot sector
A term used to describe a special-purpose block of data on a disk or partition essential to the boot process of an x86 computer. The computer's BIOS will process the boot sector of the MBR initially to find a partition to continue the boot process. The first sector of that partition or volume contains a boot sector with code responsible for beginning the operating system load process from a partition or volume.
cluster
A unit of storage for reading and writing file data in a file system. The cluster size is determined when a partition or volume is first formatted with a file system. Cluster size is based on the sector size of a disk and the number of sectors used per cluster. Cluster sizes typically range from 512 bytes to 64 KB.
defragmentation
The process of ordering data on the hard disk in a contiguous fashion to minimize the delays in reading or writing data. This attempts to minimize the mechanical delay caused by having to move read/write mechanisms from one region of the disk to another.
Disk Management console
An MMC console snap-in used to administer hard disks in Windows 7.
drive letter
A letter of the alphabet assigned to a formatted partition or volume as a reference point for future access by the user or their applications.
dynamic disk
A new method used to organize disk space into volumes. First introduced with Windows 2000, the dynamic disk method is seen as an improvement over basic disk technology. Not all operating systems support the dynamic disk method of organizing disk space. This may restrict multiboot configurations. Dynamic disk technology supports simple, spanned, striped, mirrored, and RAID 5 volumes. All dynamic disks in a computer are identified with a group membership ID personalized for the computer they belong to. Volume information is stored in a database that is replicated to all other dynamic disks in the computer. The volume information database is stored in the last 1 MB of each disk.
extended partition
A reserved block of space on a basic disk. No more than one extended partition can exist on a single basic disk. Logical partitions are created within the extended partition. Extended partitions cannot be formatted with a file system directly.
File Allocation Table (FAT)
A file system used to organize files and folders in a partition or volume. A master File Allocation Table is used to indicate what files and folders exist within the file system. The FAT table entries point to the beginning cluster used to store a file's data. The first cluster points to the next cluster used to store the next part of the file's data.
The file's data is stored in a chain of clusters, with the last cluster marked with an end-of-file identifier. The FAT table stores the name and attributes of the files and folders on the disk, their starting cluster, and which clusters link to the next. The number of addressable clusters determines the size of the FAT table. The limit for how many addressable clusters exist is based on the size of the binary number used to address each cluster. The number of bits used for the cluster address distinguishes the different versions of FAT. The common versions of FAT include FAT16 and FAT32.
FAT
See File Allocation Table.
Foreign Disk
A dynamic disk that is recognized as not belonging to the computer it is currently installed in. Until the disk is imported, to change its dynamic disk computer membership, the volumes it contains are not accessible.
logical partition
A reserved block of space on a basic disk. Logical partitions can only be created within an extended partition. As long as free space exists in an extended partition, a new logical partition can be created. Logical partitions can be formatted with a file system directly.
Master Boot Record (MBR)
The Master Boot Record exists at the very first sector of an IBM-formatted hard disk. It contains code to start the load process for an operating system from a partition or volume on the disk, a partition table to indicate what space has been reserved as partitions, and a signature sequence of bytes used to identify the disk to the operating system. When the disk is used as a basic disk, the partition table is used to identify primary, extended, and logical partition types. When the disk is used as a dynamic disk, the partition table is filled with placeholder values and the volume information is actually held in a 1 MB dynamic volume database at the end of the drive.
mirrored volume
A RAID 1 implementation using dynamic disks.
mount point
An empty folder in an NTFS-formatted file system that is used to point to another FAT, FAT32, or NTFS partition.
New Technology File System (NTFS)
A file system introduced with Windows NT. NTFS supports advanced features to add reliability, security, and flexibility that file systems such as FAT and FAT32 do not have.
NTFS
See New Technology File System.
partition table
A data structure contained in the MBR that is used to identify reserved areas of disk space for hard disks formatted for x86 computers. The partition table holds a maximum of four entries originally tasked to point to a maximum of four primary partitions, or three primary and one extended partitions.
primary partition
A reserved region of disk space on a basic disk that is capable of loading an operating system. The first sector of the primary partition is also known as a boot sector and stores the code for beginning the operating system load process from that primary partition.
RAID 0
A collection of disks that combine their storage capacity by striping data across all drives. Data is written in a fixed block size, typically sized in KB, in a sequential fashion to each disk. The first block of data for a file is written to the first disk, the second block of data to the second disk, and so on until the last drive is reached. The next block of data starts over with the first drive, and the process continues with each subsequent block of data written to the next disk. This type of storage is not fault tolerant, and the failure of a single disk will result in the loss of all file data. This type of storage will generally improve write and read performance when compared with a single disk. The number of disks that can be pooled this way is limited by the operating system or hardware controller used to pool the disks.
RAID 1
Two disks are used to store a single copy of file data in a fault-tolerant fashion. An exact copy of the data is written to each disk. If one disk fails, the other copy allows continued operation. Performance is similar to a single disk where reads are generally faster and writes can be slower. Both disks can be on a single controller, which introduces a common point of failure. If the hardware used to control each disk is fully duplicated into independent channels, the system is referred to as a duplexed mirror.
RAID 5
A collection of disks that combine their storage capacity by striping data and error-correcting parity information across all drives. The parity information is calculated from the data itself and can be used to identify and regenerate damaged or missing data. The data and parity information is striped in the same fashion as RAID 0 data. RAID 5 is fault tolerant in that a single disk in the collection may fail and the missing data can be calculated from the remaining data and parity information distributed across the remaining disks. A multiple disk failure will result in the loss of all data in the collection. The disks space cost for parity information is approximately the same as the size of disks space contributed from one disk member. For example, if five 10 GB disks are collected into a single RAID 5 solution then the space of one disk, 10 GB, is consumed by parity information. The remainder of 40 GB is available for file storage. A minimum of three disks is required to build a RAID 5 solution.
Redundant Array of Independent Disks (RAID)
A standard reference to a collection of disks grouped to store data. The RAID level indicates the type of grouping and is indicated by a number following the term RAID. Common RAID levels are RAID 0 striped storage, RAID 1 mirrored storage, and RAID 5 striped storage with error-correcting information.
removable disk storage
A mass storage device that can be removed from the computer, either by powering down the computer first or while the computer is running. This includes floppy disks, portable hard disks, and cartridge-based disk storage.
sector
A single unit of storage for a hard disk that represents the smallest block of data that can be read or written to the disk. The typical hard disk sector size is 512 bytes.
simple volume
A reserved area of space on a single dynamic disk. A simple volume can be formatted with a file system. The areas of space reserved for a simple volume do not have to be contiguous on the dynamic disk.
spanned volume
A reserved area of space combined from two or more dynamic disks. A spanned volume can be formatted with a file system. Files are written to each disk's reserved area of space until that area is full. Additional file data is then written to the next available reserved area of space on the next disk that is part of the spanned volume. The capacity of the spanned volume is the total of all reserved areas of space from each disk that is a member of the spanned volume. Loss of a single disk that holds part of the spanned volume will result in the total loss of the volume.
striped volume
A RAID 0 implementation using dynamic disks.
system partition
The partition or volume used to initiate the boot sequence for a computer from a hard disk. The system partition is processed before the boot partition, which loads the remainder of the operating system. The system partition can be the same partition as the boot partition.
volume
A term used to refer to a region of disk space reserved to store file data. The term is used to generically refer to both dynamic disk volumes and basic disk partitions.
x86
A generic term used to refer to computers based on Intel CPU processors. These CPUs include 8086, 80286, 80386, 80486, the Pentium family and Pentium compatible processors from other companies such as AMD.