Hard Disk Drive

How data is organised on the platter:

Track

The disks surface is divided into concentric series of circles called tracks.

Sector

A sector is the smallest unit of data that can be read or written from a disk. Typically, sectors are 512 bytes in size, but other sizes including 1024 and 2048 are also common. [1]

Cluster

The term used for a number of contiguous (next to each other) sectors.

Cylinder

A cylinder is the same track on all platters.

Access Time

Access time is the amount of time taken to retrieve data from the hard drive.  It consists of two parts:

Seek Time

Seek time is the time taken for the head to move to the correct track.

Latency

Latency is the time taken for the platter to spin round to the correct sector.

Data Organisation

FAT

The File Allocation Table (FAT) is used by the operating system to access the Hard Drive.  It contains entries for every addressable cluster on the Hard Drive and the operating system uses it to manage additions, deletions and changes to the data stored on the disc.

NTFS

New Technology File System (NTFS) is one of the file systems supported by Microsoft Operating Systems since Windows NT.  It is an improvement over previous file systems, such as FAT-16 and FAT-32, as it has features to improve reliability, such as transaction logs to help recover from disk failures.  To control access to files, you can set permissions for directories and/or individual files.

Defragment

Defragmenting your hard disk is a great way to boost the performance of your computer.  Adding and deleting files from your hard disk is a common task. Unfortunately, this process is not always done very efficiently. For example, when you delete a bunch of little files and add a new large file, the file may get broken up into mulitple sections on the hard disk. The computer will still read the newly added file as a single valid file, but the drive will have to scan multiple parts of the disk to read it. Because hard disk seek time is one of the most significant bottlenecks in a computer's performance, this can drag down your computer's speed quite a bit. If you have a lot of "fragmented" files on your hard disk, your computer may slow down as you wait for your hard-drive to read files.