Segment - Revision history

Jnc: fix link

2019-11-22T20:36:30Z

fix link

Jnc: +cat

2018-12-15T19:33:27Z

+cat

Jnc: Proper cat, clarify a bit

2018-10-21T12:32:19Z

Proper cat, clarify a bit

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

Jnc: Expand discussion on uses

2018-04-16T15:39:47Z

Expand discussion on uses

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

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.

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 ==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.

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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==
@@ Line 7: / Line 7: @@
 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}}

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