Disk storage is a general category of a computer storage mechanisms, in which data is recorded on planar, round and rotating surfaces (disks, discs, or platters). Computer data storage, often called storage or memory, refers to Computer components devices and recording media that retain digital A disk drive is a peripheral device used to collect information from. In Computer hardware, a peripheral device is any device attached to a computer in order to expand its functionality (basically input and output devices together are known Main implementations are hard disks, floppy disks and optical discs. A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased Nowadays the term disk storage almost exclusively refers to hard disk storage.
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History
In the 1950s and the early 1960s single data bits were stored as magnetic charges in a magnetic core memory. The 1950s Decade refers to the years of 1950 to 1959 inclusive The 1960s decade refers to the years from the beginning of 1960 to the end of 1969 A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Magnetic core memory, or ferrite-core memory, is an early form of Random access Computer memory.
Then the scientists at IBM in San Jose, California created a rotating drum that was coated in a magnetically polarizable film that could be used to store data by changing and sensing magnetic polarization. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology The drum was later superseded by disks, because of their lower mass and inertia. Rey Johnson, an inventor who worked for IBM for many years, is said to be the "father" of the disk drive. Reynold "Rey" Johnson (1906-1998 was an American inventor and computer pioneer
The random-access, low-density storage of disks was developed to complement the already used sequential-access high-density storage provided by magnetic tape. In Computer science, sequential access means that a group of elements (e Magnetic tape is a medium for Magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of Plastic. Vigorous innovation in disk storage technology, coupled with less vigorous innovation in tape storage, has reduced the density and cost per bit gap between disk and tape, reducing the importance of tape as a complement to disk.
Audio recordings
In musical and audio data storage, the first devices were also drum shaped, called phonograph cylinders, which were popularized by Thomas Edison. Music is an Art form in which the medium is Sound organized in Time. The earliest method of recording and reproducing sound was on phonograph cylinders. In the 1910s these were replaced as the dominant medium of sound recording by analogue disc records, commonly called gramophone records (in British English) or phonograph records (in American English). The 1910s decade ran from January 1 1910 through December 31 1919 A gramophone British English or UK English ( BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the Phonology North American English regional phonology In many ways compared to English English, North American English is conservative in its Phonology. From the 1950s through the 1980s, audio recordings were also done on magnetic tape media of several types, although the vinyl record remained the most popular medium for home use. The 1950s Decade refers to the years of 1950 to 1959 inclusive The 1980s was the decade spanning from January 1 1980 to December 31 1989. Magnetic tape is a medium for Magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of Plastic. A gramophone These were mostly replaced by compact disc technology, where the data is recorded in a digital format as optical information. A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio This compact disc technology has been widely accepted, and data storage, using writable compact disks or CD-R devices is very common. A CD-R ( C ompact D isc- R ecordable is a variation of the Compact Disc invented by Philips and Sony.
Access methods
In disk storage, there are the two primary access methods. Block storage (or raw disk storage) means that the disk is divided into blocks which are addressed by number, like on a magnetic tape. In Computing (specifically data transmission and data storage) block is a sequence of Bytes or Bits having a nominal length (a block size Magnetic tape is a medium for Magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of Plastic. File storage contains an abstraction of files and directories which can be addressed by name. In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make In Computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time Another access method, content-addressable storage (CAS) uses a hashing algorithm to refer to pieces of data. Content-addressable memory (CAM is a special type of computer memory used in certain very high speed searching applications
Basic terminology
- Rotation - how the disks spin. Two techniques are common:
- Constant angular velocity (CAV) keeps the disk spinning at a fixed rate, measured in revolutions per minute (RPM). In Optical storage, constant angular velocity (CAV is a qualifier for the rated speed of an Optical disc drive, and may also be applied to the writing speed of recordable This means the heads cover more distance per unit of time on the outer tracks than on the inner tracks. This method is typical with computer hard drives.
- Constant linear velocity (CLV) keeps the distance covered by the heads per unit time fixed. In Optical storage, constant linear velocity (CLV is a qualifier for the rated speed of an Optical disc drive, and may also be applied to the writing speed of recordable Thus the disk has to slow down as the arm moves to the outer tracks. This method is typical for CD drives. A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio
- Sector - an area of disk enclosed within a given central angle (a pie piece)
- Platter - an individual disk (since confusingly, what is now commonly called a single hard disk is in fact a set of disks)
- Head - the device that reads and writes the information - magnetic or optical - on the disk surface. In the context of Computer Disk storage, a sector is a subdivision of a track (Figure 1 item A on a Magnetic disk or Optical disc
- Arm - the mechanical assembly that supports the head as it moves in and out.
- Seek time - average time needed to move the head to a new position. Seek time is one of the three delays associated with reading or writing Data on a Computer 's Disk drive, and somewhat similar for CD or
- Rotational delay - average time, once the arm is on the right track, before a head is over a desired sector. Rotational delay is one of the three delays associated with reading or writing data on a computer's disk drive, and somewhat similar for CD or DVD drives
- Interleave - the spacing between sectors. Since early hard disks had enough buffer space to read only one sector at a time, sequential sectors were physically spaced on the media to enable the next sector to be in the correct position under the head once the host was ready to read it. At an interleave factor of 3:1, three full rotations would be required to read an entire track. Almost all hard disks since Compaq and Western Digital defined the AT Attachment standard have however used an interleave factor of 1:1. Compaq Computer Corporation was an American Personal computer company founded in 1982 and is now a brand name of Hewlett-Packard. Western Digital Corporation ( (often abbreviated to WD) is a manufacturer of computer hard disk drives, and has a long history in the electronics industry as AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state Floppy disks are still usually interleaved.
See also
- Computer data storage
- Compact disc
- Early IBM disk storage
- Floppy disk
- Hard disk
- Fragmentation (computer)
- Solid-state drive
- Information repository
- Data proliferation
- RAID
- Perpendicular recording
External links
- More Bits in Pits - article by JR Minkel
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