Files are simply long lines of bits stored in the physical storage of a computer system. Space on disc is allocated to files and then information regarding these files is recorded in the "directory" file which is typically stored at the beginning of the disc (or volume).

The system "bootstrap" program is also normally stored at the beginning of the disc. The bootstrap and directory files need to be found simply becasue they need to be used before any complex programs such as the Operating System are loaded into memory. Storing them at the beginning of the disc therefore makes this task easier.

The directory information consists of the files' name, type, owner, access flags (e.g. protected, private, public etc...), creation date, and location (i.e. the sectors it occupies on disc).

The File Allocation Table (FAT) and Disk Usage Map are stored in a large hidden file. These are used to manage how the disc is divided up and where files / data is put on it. A 16-bit FAT (FAT16) was originally used for hard discs in computers several years ago but FAT32 was introduced due to the fact that hard disks were becoming much larger and bigger File Allocation Tables were needed to successfully manage them.

Disks become fragmented over time as they are used. As files stored on a disk are created, changed, and deleted, the data becomes spread out and dispersed into small chunks across the whole disk. This eventually causes the process of retrieving data (through serial access) to be dramatically slowed down.

Large hard disks have a fixed size FAT. If they did not, the FAT could become very large as data could be spread out through the disk in a very complex manner leading to a large number of storage "blocks" that are recorded in the FAT. To keep the FAT limited in size, but still able to manage a whole disk, it assigns ranges of sectors (or blocks) to files instead of allocating every single sector to a file or part of a file for example.

A directory hierarchy allows files to be organised so that they can be accessed faster. A typical directory hierarchy may have a "Temp" folder (or directory) to store temporary system files for example, a "Documents" folder, a "Programs" folder, and a folder for the operating system files (e.g. "Windows").

Index files are used to find records that are stored in a file. This is similar to the way that the directory file indexes the disk so that files stored on it can be found easily.

Disks involve the reading or writing of data to a circular disc which spins on its axis. The head which reads and writes the data can move radially from the centre to the outer circumference of the disc. Moving in this manner switches between which track is being read from the disc. The "seek time" is the time taken for the head to move so that data can be read from the disc.

A 3 1/2 inch disk has 2 surfaces (or sides) with 80 tracks of data. There are 18 sectors of 512Kb each. Therefore, the disk can store (2x80x18x512 =) 1440KB or 1.44MB. With a rotation speed of 300rpm, the data transfer rate (in KB/s) is 300/60 x 18 x 512 = 46KB/s

Hard disks can store much more data than this (Gigabytes) and can access this data at a much faster rate (many Megabytes per second).

Compared to main / internal memory though, hard disk storage is much slower at accessing data. Internal memory is volatile opposed to mass disk storage which can permanently store data. Hard disk storage is much cheaper than internal memory.

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