Disk - Revision history

Jnc: Add 'moving-head disk' name

2025-07-17T14:51:11Z

Add 'moving-head disk' name

← Older revision		Revision as of 14:51, 17 July 2025
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	With the head at a fixed position, it writes a circular '''track'''. Some early disks had a separate head for each track; such disks were known as [[fixed-head disk]]s.		With the head at a fixed position, it writes a circular '''track'''. Some early disks had a separate head for each track; such disks were known as [[fixed-head disk]]s.

	For most disks, a head is shared between tracks; a separate mechanism is used to move the head in and out, a process known as '''seeking'''. The drive can write data on many tracks, each at a fixed distance from its neighbours. This is mechanically more complex, but uses fewer components overall.		For most disks, a head is shared between tracks; a separate mechanism is used to move the head in and out (leading to their name, '''moving-head disks'''), a process known as '''seeking'''. The drive can write data on many tracks, each at a fixed distance from its neighbours. This is mechanically more complex, but uses fewer components overall.

	Many disks have more than one platter, each with its own read-write heads (usually two, one for each surface), and the collection of tracks at a given offset is referred to as a '''cylinder'''.		Many disks have more than one platter, each with its own read-write heads (usually two, one for each surface), and the collection of tracks at a given offset is referred to as a '''cylinder'''.

Vaxorcist: Some additions, e.g. Formula for disk capacity

2023-07-16T12:20:14Z

Some additions, e.g. Formula for disk capacity

← Older revision		Revision as of 12:20, 16 July 2023
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	'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of rotating [[magnetic storage]], [[drum]]s.		'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of rotating [[magnetic storage]], [[drum]]s.

	All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating. A read/write [[head]] is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.		All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating. A read/write '''[[head]]''' is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.

	In most disks, the platter rotates at high speed, and the heads are shaped to ride on a thin film of air at a very low altitude above the surface of the platter (a small spacing is required to maximize the density of the data on the platter; the smaller the spacing, the more densely the information can be written).		In most disks, the platter rotates at high speed, and the heads are shaped to ride on a thin film of air at a very low altitude above the surface of the platter (a small spacing is required to maximize the density of the data on the platter; the smaller the spacing, the more densely the information can be written).
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	Many disks have more than one platter, each with its own read-write heads (usually two, one for each surface), and the collection of tracks at a given offset is referred to as a '''cylinder'''.		Many disks have more than one platter, each with its own read-write heads (usually two, one for each surface), and the collection of tracks at a given offset is referred to as a '''cylinder'''.

	A complete track usually contains more data than can easily be read and written as an un-divided unit, and so tracks are usually divided divided up into a number of '''sectors''' or '''blocks'''. This division may be purely logical, and indicated in the magnetic pattern written to the disk, or there may be actual physical means of indicating where each block is. There is also an intermediate (used in most [[floppy disk]]s), where there is a physical mark to indicate the start of the track, but the sectors are logical.		A complete track usually contains more data than can easily be read and written as an un-divided unit, and so tracks are usually divided divided up into a number of '''sectors''' or '''blocks'''. This division may be purely logical, and indicated in the magnetic pattern written to the disk, or there may be actual physical means of indicating where each block is. There is also an intermediate (used in most [[floppy disk]]s), where there is a physical mark to indicate the start of the track, but the sectors are logical. Sectors are usually sized to 256 or 512 byte, depending on the controller and/or software used to write the sector info (called 'low-level format') to disk. Sometimes it is even possible to set the sector density (given in 'sectors per track').

	Most early disk drives used '''packs''', a group of one or more platters which could be installed or removed in a drive, in a process called '''mounting''' a pack. So a system could have multiple packs (for backup purposes, or for infrequently needed data) which could be stored until needed.		Most early disk drives used '''packs''', a group of one or more platters which could be installed or removed in a drive, in a process called '''mounting''' a pack. So a system could have multiple packs (for backup purposes, or for infrequently needed data) which could be stored until needed.
Line 24:		Line 24:

	The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).		The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).

			==Disk capacity==

			The formula to calculate disk capacity in byte is:

			disk capacity = (byte/sector) * (sectors/track) * (tracks/cylinder) * cylinders

			This calculation is only valid for disks with constant sector density; which is no longer the case for more recent disks.

	==Recent developments==		==Recent developments==

Jnc: typo

2020-12-20T22:42:38Z

typo

← Older revision		Revision as of 22:42, 20 December 2020
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	More recently, to increase the amount of information stored on a drive, most disk drives are now sealed. The disks in modern [[personal computer]]s are generally referred to as '''hard drives''' (to distinguish them from the floppy drives which were all the earliest PC's were equipped with).		More recently, to increase the amount of information stored on a drive, most disk drives are now sealed. The disks in modern [[personal computer]]s are generally referred to as '''hard drives''' (to distinguish them from the floppy drives which were all the earliest PC's were equipped with).

	==External links=		==External links==

	* [http://chmhdd.wikifoundry.com/ Hard Disk Drive History]		* [http://chmhdd.wikifoundry.com/ Hard Disk Drive History]

	[[Category: Device Basics]]		[[Category: Device Basics]]

Jnc: +ext link

2020-12-20T22:41:28Z

+ext link

← Older revision		Revision as of 22:41, 20 December 2020
Line 28:		Line 28:

	More recently, to increase the amount of information stored on a drive, most disk drives are now sealed. The disks in modern [[personal computer]]s are generally referred to as '''hard drives''' (to distinguish them from the floppy drives which were all the earliest PC's were equipped with).		More recently, to increase the amount of information stored on a drive, most disk drives are now sealed. The disks in modern [[personal computer]]s are generally referred to as '''hard drives''' (to distinguish them from the floppy drives which were all the earliest PC's were equipped with).

			==External links=

			* [http://chmhdd.wikifoundry.com/ Hard Disk Drive History]

	[[Category: Device Basics]]		[[Category: Device Basics]]

Jnc: +cat

2018-12-13T14:40:36Z

+cat

← Older revision		Revision as of 14:40, 13 December 2018
Line 1:		Line 1:
	'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of [[magnetic storage]], [[drum]]s.		'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of rotating [[magnetic storage]], [[drum]]s.

	All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating. A read/write [[head]] is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.		All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating. A read/write [[head]] is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.
Line 28:		Line 28:

	More recently, to increase the amount of information stored on a drive, most disk drives are now sealed. The disks in modern [[personal computer]]s are generally referred to as '''hard drives''' (to distinguish them from the floppy drives which were all the earliest PC's were equipped with).		More recently, to increase the amount of information stored on a drive, most disk drives are now sealed. The disks in modern [[personal computer]]s are generally referred to as '''hard drives''' (to distinguish them from the floppy drives which were all the earliest PC's were equipped with).

			[[Category: Device Basics]]

Jnc: /* Low-cost disks */ minor tweak

2018-10-19T12:10:14Z

Low-cost disks: minor tweak

← Older revision		Revision as of 12:10, 19 October 2018
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	Initially, all disks used large metal platters (usually aluminium), complex mechanisms to move the heads in and out at high speed (to reduce seek times), and were generally fairly expensive.		Initially, all disks used large metal platters (usually aluminium), complex mechanisms to move the heads in and out at high speed (to reduce seek times), and were generally fairly expensive.

	In the late 1960's, IBM developed a new form of disk, the ~~'''~~floppy ~~drive'''~~, which used instead a 'platter' of mylar (a stiff plastic); this was much cheaper, but at significantly lower performance. In ~~these~~ drives, the disk rotates much more slowly, and the head makes contact with the surface.		In the late 1960's, IBM developed a new form of disk, the [[floppy disk]], which used instead a 'platter' of mylar (a stiff plastic); this was much cheaper, but at significantly lower performance. In their drives, the disk rotates much more slowly, and the head makes contact with the surface.

	The rotating substrate - not referred to as platters, but called the 'magnetic medium' was carried in a stiff plastic envelope, with a thin felt layer on the inside (to keep the medium clean). The entire assembly is usually referred to as a [[floppy disk]] (or 'floppy' for short; the term 'diskette' was also used).		The rotating substrate - not referred to as platters, but called the 'magnetic medium' was carried in a stiff plastic envelope, with a thin felt layer on the inside (to keep the medium clean). The entire assembly is usually referred to as a 'floppy disk' (or 'floppy' for short; the term 'diskette' was also used).

	The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).		The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).

Jnc: More common term

2018-09-04T13:04:58Z

More common term

← Older revision		Revision as of 13:04, 4 September 2018
Line 21:		Line 21:
	In the late 1960's, IBM developed a new form of disk, the '''floppy drive''', which used instead a 'platter' of mylar (a stiff plastic); this was much cheaper, but at significantly lower performance. In these drives, the disk rotates much more slowly, and the head makes contact with the surface.		In the late 1960's, IBM developed a new form of disk, the '''floppy drive''', which used instead a 'platter' of mylar (a stiff plastic); this was much cheaper, but at significantly lower performance. In these drives, the disk rotates much more slowly, and the head makes contact with the surface.

	The rotating substrate - not referred to as platters, but called the 'magnetic medium' was carried in a stiff plastic envelope, with a thin felt layer on the inside (to keep the medium clean). The entire assembly is usually referred to as a [[~~diskette\|~~floppy disk]] (or 'floppy' for short).		The rotating substrate - not referred to as platters, but called the 'magnetic medium' was carried in a stiff plastic envelope, with a thin felt layer on the inside (to keep the medium clean). The entire assembly is usually referred to as a [[floppy disk]] (or 'floppy' for short; the term 'diskette' was also used).

	The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).		The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).

Jnc: /* Low-cost disks */ Sighten out floppy drive/disk terminology

2017-10-25T14:18:41Z

Low-cost disks: Sighten out floppy drive/disk terminology

← Older revision		Revision as of 14:18, 25 October 2017
Line 19:		Line 19:
	Initially, all disks used large metal platters (usually aluminium), complex mechanisms to move the heads in and out at high speed (to reduce seek times), and were generally fairly expensive.		Initially, all disks used large metal platters (usually aluminium), complex mechanisms to move the heads in and out at high speed (to reduce seek times), and were generally fairly expensive.

	In the late 1960's, IBM developed a new form of disk, the [[floppy ~~disk]]~~, which used instead a 'platter' of mylar (a stiff plastic); this was much cheaper, but at significantly lower performance. ~~These disks rotate~~ much more slowly, and the head makes contact with the surface.		In the late 1960's, IBM developed a new form of disk, the '''floppy drive''', which used instead a 'platter' of mylar (a stiff plastic); this was much cheaper, but at significantly lower performance. In these drives, the disk rotates much more slowly, and the head makes contact with the surface.

	The rotating substrate - not referred to as platters, but called the 'magnetic medium'~~, or 'floppy' (although that latter term usually refers to the entire assembly)~~ was carried in a stiff plastic envelope, with a thin felt layer on the inside (to keep the medium clean).		The rotating substrate - not referred to as platters, but called the 'magnetic medium' was carried in a stiff plastic envelope, with a thin felt layer on the inside (to keep the medium clean). The entire assembly is usually referred to as a [[diskette\|floppy disk]] (or 'floppy' for short).

	The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).		The first floppies were 8 inches in diameter; later they were produced in 5-1/4 inch, and finally 3-1/2 inch sizes (the latter in rigid plastic containers).

Jnc: link, move content

2017-09-30T12:59:54Z

link, move content

← Older revision		Revision as of 12:59, 30 September 2017
Line 1:		Line 1:
	'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of magnetic storage, [[drum]]s.		'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of [[magnetic storage]], [[drum]]s.

	All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating ~~- very fine particles of magnetic material mixed with a binder, which caused the coating to adhere to the platter~~. A read/write [[head]] is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.		All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating. A read/write [[head]] is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.

	In most disks, the platter rotates at high speed, and the heads are shaped to ride on a thin film of air at a very low altitude above the surface of the platter (a small spacing is required to maximize the density of the data on the platter).		In most disks, the platter rotates at high speed, and the heads are shaped to ride on a thin film of air at a very low altitude above the surface of the platter (a small spacing is required to maximize the density of the data on the platter; the smaller the spacing, the more densely the information can be written).

	With the head at a fixed position, it writes a circular '''track'''. Some early disks had a separate head for each track; such disks were known as [[fixed-head disk]]s.		With the head at a fixed position, it writes a circular '''track'''. Some early disks had a separate head for each track; such disks were known as [[fixed-head disk]]s.

Jnc: Say a bit moreabout sectors/blocks

2017-09-29T13:31:23Z

Say a bit moreabout sectors/blocks

← Older revision		Revision as of 13:31, 29 September 2017
Line 1:		Line 1:
	'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers.		'''Disk''' storage was, until recently, the primary form of high-speed on-line [[secondary storage]] for computers. Disks replaced an earlier form of magnetic storage, [[drum]]s.

	All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating - very fine particles of magnetic material mixed with a binder, which caused the coating to adhere to the platter. A read/write head~~, identical in basic concept to the head on a magnetic tape recorder,~~ is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.		All disk storage is basically the same; a circular '''platter''' is coated with a magnetic coating - very fine particles of magnetic material mixed with a binder, which caused the coating to adhere to the platter. A read/write [[head]] is used to read and write data on the disk as the disk is rotated underneath (or above) it, by magnetizing the particles in one of two directions.

	~~A separate mechanism is used to move the head in and out~~, ~~a process known as '''seeking'''. With~~ the ~~head~~ at ~~a fixed position~~, ~~it writes a circular '''track''';~~ the ~~drive can write data~~ on ~~many tracks, each~~ at a ~~fixed distance from its neighbours. Many disks have more than one~~ platter~~, each with its own read-write heads~~ (~~usually two, one for each surface), and the collection of tracks at~~ a ~~given offset~~ is ~~referred~~ to ~~as a '''cylinder'''. Each track is usually divided into a number~~ of ~~'''sectors''' - a complete track usually contains too much~~ data ~~to be usefully read and written as a complete unit~~.		In most disks, the platter rotates at high speed, and the heads are shaped to ride on a thin film of air at a very low altitude above the surface of the platter (a small spacing is required to maximize the density of the data on the platter).

	~~The platter rotates~~ at ~~high speed~~, ~~and the heads are shaped to ride on a thin film of air at~~ a ~~very low altitude above the surface of the platter (~~a ~~small spacing is required to maximize the density of the data on the platter)~~.		With the head at a fixed position, it writes a circular '''track'''. Some early disks had a separate head for each track; such disks were known as [[fixed-head disk]]s.

	~~Some early~~ disks ~~had~~ a separate head ~~for each track; such disks were~~ known as [[fixed-~~head disk]]s~~. ~~Disks replaced~~ an ~~earlier form~~ of magnetic ~~storage~~, [[~~drum~~]]s.		For most disks, a head is shared between tracks; a separate mechanism is used to move the head in and out, a process known as '''seeking'''. The drive can write data on many tracks, each at a fixed distance from its neighbours. This is mechanically more complex, but uses fewer components overall.

			Many disks have more than one platter, each with its own read-write heads (usually two, one for each surface), and the collection of tracks at a given offset is referred to as a '''cylinder'''.

			A complete track usually contains more data than can easily be read and written as an un-divided unit, and so tracks are usually divided divided up into a number of '''sectors''' or '''blocks'''. This division may be purely logical, and indicated in the magnetic pattern written to the disk, or there may be actual physical means of indicating where each block is. There is also an intermediate (used in most [[floppy disk]]s), where there is a physical mark to indicate the start of the track, but the sectors are logical.

	Most early disk drives used '''packs''', a group of one or more platters which could be installed or removed in a drive, in a process called '''mounting''' a pack. So a system could have multiple packs (for backup purposes, or for infrequently needed data) which could be stored until needed.		Most early disk drives used '''packs''', a group of one or more platters which could be installed or removed in a drive, in a process called '''mounting''' a pack. So a system could have multiple packs (for backup purposes, or for infrequently needed data) which could be stored until needed.