Index register - Revision history

Jnc: better

2018-12-15T14:16:29Z

better

Jnc: typo

2018-12-13T03:15:07Z

typo

Jnc: +cat

2018-12-13T03:14:24Z

+cat

Jnc: A good start

2018-05-12T13:54:23Z

A good start

New page

An '''index register''' is a [[register]] in a [[Central Processing Unit|CPU]] which, duing the execution of an [[instruction]], can be added to something else (perhaps a constant in the instruction, or sometimes another register) to produce the [[address]] of an operand in [[main memory]]. They are useful for walking along an [[array]], applying some operation to all the elements in it.

In early computers, such addresses had to be computed 'manually'; in some very earliest computers, which could not use register contents as an address, it was necessary to use [[self-modifying code]] to process an array.

In early computers with index registers (such as the [[IBM 704]] and descendants), they were special registers dedicated to this function; in modern computers, generally any of the machine's [[general register]]s can be used as an index register.

← Older revision		Revision as of 14:16, 15 December 2018
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	In early computers with index registers (such as the [[IBM 704]] and descendants), they were special registers dedicated to this function; in modern computers, generally any of the machine's [[general register]]s can be used as an index register.		In early computers with index registers (such as the [[IBM 704]] and descendants), they were special registers dedicated to this function; in modern computers, generally any of the machine's [[general register]]s can be used as an index register.

−	[[Category: ~~Hardware~~ Basics‎‎]]	+	[[Category: CPU Basics‎‎]]

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 An '''index register''' is a [[register]] in a [[Central Processing Unit|CPU]] which, duing the execution of an [[instruction]], can be added to something else (perhaps a constant in the instruction, or sometimes another register) to produce the [[address]] of an operand in [[main memory]].
- They are useful for walking along an [[array]], applying some operation to all the elements in it. In early computers, such addresses had to be computed 'manually'; in some very earliest computers, which could not use register contents as an address, it was necessary to use [[self-modifying code]] to process an array.
+They are useful for walking along an [[array]], applying some operation to all the elements in it. In early computers, such addresses had to be computed 'manually'; in some very earliest computers, which could not use register contents as an address, it was necessary to use [[self-modifying code]] to process an array.
 In early computers with index registers (such as the [[IBM 704]] and descendants), they were special registers dedicated to this function; in modern computers, generally any of the machine's [[general register]]s can be used as an index register.
 [[Category: Hardware Basics‎‎]]