Segment - Revision history

Jnc: fix link

2019-11-22T20:36:30Z

fix link

← Older revision		Revision as of 20:36, 22 November 2019
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	==Uses==		==Uses==

	Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture]]), but this usage is often somewhat of a kludge, a way to expand the amount of memory accessible to an existing CPU architecture later in its life.		Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture), but this usage is often somewhat of a kludge, a way to expand the amount of memory accessible to an existing CPU architecture later in its life.

	Generally the preferred approach is to simply give a CPU a larger linear address space; this generally means making [[word]], and [[instruction]], sizes larger, which was not always an economically viable option when [[main memory]] was much smaller, and much more expensive. (For example, in the [[PDP-8]].)		Generally the preferred approach is to simply give a CPU a larger linear address space; this generally means making [[word]], and [[instruction]], sizes larger, which was not always an economically viable option when [[main memory]] was much smaller, and much more expensive. (For example, in the [[PDP-8 family]].)

	Segmentation is also used in building [[single-level store]] systems, where it is a much more natural tool. It ''is'' however ''possible'' to build such systems with CPUs which support only a very large 'flat' address space, mapping the SLS' segments into blocks of that address space.		Segmentation is also used in building [[single-level store]] systems, where it is a much more natural tool. It ''is'' however ''possible'' to build such systems with CPUs which support only a very large 'flat' address space, mapping the SLS' segments into blocks of that address space.

Jnc: +cat

2018-12-15T19:33:27Z

+cat

← Older revision		Revision as of 19:33, 15 December 2018
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	{{semi-stub}}		{{semi-stub}}

			[[Category: CPU Basics]]

Jnc: Proper cat, clarify a bit

2018-10-21T12:32:19Z

Proper cat, clarify a bit

← Older revision		Revision as of 12:32, 21 October 2018
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	'''Segmentation''' (using '''segments''') is an enhancement to the memory naming semantics of some [[Central Processing Unit\|CPU]] [[architecture]]s. Segments are blocks of memory identified by a '''segment number'''.		'''Segmentation''' (using '''segments''') is an enhancement to the memory naming semantics of some [[Central Processing Unit\|CPU]] [[architecture]]s. Segments are blocks of [[main memory]] identified by a '''segment number'''.

	Most CPUs support a linear (single axis) [[address space]]; memory locations are defined by a single number, the address. With segmentation, the CPU's address space can best be seen as a two-axis matrix: the segment number on one axis, and then the offset [[byte]]/[[word]] within the segment on the other; memory locations are named by a tuple (segment and offset).		Most CPUs support a linear (single axis) [[address space]]; memory locations are defined by a single number, the [[address]]. With segmentation, the CPU's address space can best be seen as a two-axis matrix: the segment number on one axis, and then the offset [[byte]]/[[word]] within the segment on the other; memory locations are named by a tuple (segment and offset).

	==Uses==		==Uses==
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	Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture]]), but this usage is often somewhat of a kludge, a way to expand the amount of memory accessible to an existing CPU architecture later in its life.		Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture]]), but this usage is often somewhat of a kludge, a way to expand the amount of memory accessible to an existing CPU architecture later in its life.

	Generally the preferred approach is to simply give a CPU a larger linear address space; this generally means making word, and [[instruction]], sizes larger, which was not always an economically viable option when [[main memory]] was much smaller, and much more expensive. (For example, in the [[PDP-8]].)		Generally the preferred approach is to simply give a CPU a larger linear address space; this generally means making [[word]], and [[instruction]], sizes larger, which was not always an economically viable option when [[main memory]] was much smaller, and much more expensive. (For example, in the [[PDP-8]].)

	Segmentation is also used in building [[single-level store]] systems, where it is a much more natural tool. It ''is'' however ''possible'' to build such systems with CPUs which support only a very large 'flat' address space, mapping the segments into blocks of that address space.		Segmentation is also used in building [[single-level store]] systems, where it is a much more natural tool. It ''is'' however ''possible'' to build such systems with CPUs which support only a very large 'flat' address space, mapping the SLS' segments into blocks of that address space.

	{{stub}}		{{semi-stub}}

Jnc: Jnc moved page Segmentation to Segment over redirect: Better at the short name, easy to extend to the long version

2018-06-15T12:19:48Z

Jnc moved page Segmentation to Segment over redirect: Better at the short name, easy to extend to the long version

← Older revision		Revision as of 12:19, 15 June 2018
(No difference)

Jnc: Expand discussion on uses

2018-04-16T15:39:47Z

Expand discussion on uses

← Older revision		Revision as of 15:39, 16 April 2018
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	'''Segmentation''' (using '''segments''') is an enhancement to the ~~[[main~~ memory]] naming semantics of some [[Central Processing Unit\|CPU]] [[architecture]]s. Segments are blocks of memory identified by a '''segment number'''.		'''Segmentation''' (using '''segments''') is an enhancement to the memory naming semantics of some [[Central Processing Unit\|CPU]] [[architecture]]s. Segments are blocks of memory identified by a '''segment number'''.

	Most CPUs support a linear (single axis) [[address space]]; memory locations are defined by a single number, the address. With segmentation, the CPU's address space ~~is defined by~~ a two-axis matrix: the segment number on one axis, and then the offset byte/word within the segment on the other; memory locations are named by a tuple (segment and offset).		Most CPUs support a linear (single axis) [[address space]]; memory locations are defined by a single number, the address. With segmentation, the CPU's address space can best be seen as a two-axis matrix: the segment number on one axis, and then the offset [[byte]]/[[word]] within the segment on the other; memory locations are named by a tuple (segment and offset).

	~~Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture]], but this usage is somewhat of a kludge.~~		==Uses==

	Segmentation is also used in building [[single-level store]] systems.		Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture]]), but this usage is often somewhat of a kludge, a way to expand the amount of memory accessible to an existing CPU architecture later in its life.

			Generally the preferred approach is to simply give a CPU a larger linear address space; this generally means making word, and [[instruction]], sizes larger, which was not always an economically viable option when [[main memory]] was much smaller, and much more expensive. (For example, in the [[PDP-8]].)

			Segmentation is also used in building [[single-level store]] systems, where it is a much more natural tool. It ''is'' however ''possible'' to build such systems with CPUs which support only a very large 'flat' address space, mapping the segments into blocks of that address space.

	{{stub}}		{{stub}}

Jnc: Jnc moved page Segment to Segmentation: Writeup makes this the main term

2018-04-16T01:27:34Z

Jnc moved page Segment to Segmentation: Writeup makes this the main term

← Older revision		Revision as of 01:27, 16 April 2018
(No difference)

Jnc: A start

2018-04-16T01:26:38Z

A start

New page

'''Segmentation''' (using '''segments''') is an enhancement to the [[main memory]] naming semantics of some [[Central Processing Unit|CPU]] [[architecture]]s. Segments are blocks of memory identified by a '''segment number'''.

Most CPUs support a linear (single axis) [[address space]]; memory locations are defined by a single number, the address. With segmentation, the CPU's address space is defined by a two-axis matrix: the segment number on one axis, and then the offset byte/word within the segment on the other; memory locations are named by a tuple (segment and offset).

Segmentation has been used to expand the amount of main memory accessible to a given CPU architecture (as in the [[Intel x86]] architecture]], but this usage is somewhat of a kludge.

Segmentation is also used in building [[single-level store]] systems.

{{stub}}