Glossary

Cluster

The smallest logical unit of file storage on a hard disk. A large file's clusters can be stored in different locations on the hard disk. The hard disk's file allocation system (FAT, NTFS) keeps track of the clusters associated with a file. Even the smallest file takes up an entire cluster.

Cylinder

On a hard disk with multiple platters, the set of tracks that may be accessed without read/write head movement. That is, the collection of disk tracks on multiple platters with the same track location. Placing information that is likely to be accessed at the same time in cylinders (in the same location) reduces the head movement (seek time) and also reduces the time needed to access the information.

LBA

Logical Block Addressing is a technique used with SCSI and IDE disk drives that allows a computer to address a hard disk larger than 504 MB.

MBR

The Master Boot Record is the information in the first sector of any hard disk or diskette. It identifies how and where an operating system is located so that it can be booted (loaded) into the computer's main storage or random access memory. The MBR is executed every time the computer starts and is probably the most important data structure on the disk. The MBR contains:

the partition table for the disk
a program that reads the boot sector record of the partition containing the operating system to be booted into RAM

Sector

The smallest "pie slice" unit that can be accessed on a disk. When you low-level format a disk, the disk is divided into circular tracks and pie-shaped sectors. This is done to organize data so that it can be found by the read/write drive heads. The operating system and disk drive remember where information is stored on the disk by noting its track and sector number. Modern hard disk drives use a technique called zoned-bit recording in which tracks on the outside of the disk contain more sectors than those on the inside. A sector that cannot be used due to a physical flaw on the disk is called a bad sector.

Track

The part of a disk which passes by one read/write head while the head is stationary. The tracks are concentric circles around the disk and the sectors are segments within each circle. For example, a formatted disk might have 40 tracks, with each track divided into 10 sectors

Glossary

See Also