Base address: Difference between revisions
imported>Boleyn needs ref |
imported>Peter Flass consistency |
||
| Line 1: | Line 1: | ||
In [[computing]], a '''base address''' is a [[Memory address|address]] serving as a reference point ("base") for other addresses.<ref>{{cite web |url=https://www.wearedevelopers.com/dictionary/base-address |title=What is a base address? |website=www.wearedevelopers.com |access-date=20 June 2025}}</ref> Related addresses can be accessed using an ''addressing scheme''. | |||
In [[computing]], a '''base address''' is | |||
Under the ''relative addressing'' scheme, to obtain an [[absolute address]], the relevant base address is taken and an [[Offset (computer science)|offset]] (aka displacement) is added to it. Under this type of scheme, the base address is the lowest numbered address within a prescribed range, to facilitate adding related positive-valued offsets. | Under the ''relative addressing'' scheme, to obtain an [[absolute address]], the relevant base address is taken and an [[Offset (computer science)|offset]] (aka displacement) is added to it. Under this type of scheme, the base address is the lowest-numbered address within a prescribed range, to facilitate adding related positive-valued offsets. | ||
In [[IBM System/360 architecture]], the base address is a 24-bit value in a general register (extended in steps to 64 bits in [[z/Architecture]]), and the offset is a 12 bit value in the instruction (extended to 20 bits in z/Architecture). | In [[IBM System/360 architecture]], the base address is a 24-bit value in a general register (extended in steps to 64 bits in [[z/Architecture]]), and the offset is a 12-bit value in the instruction (extended to 20 bits in z/Architecture).<ref>{{cite book |title=Student Text Introduction to IBM System/360 Architecture |date=April 1968 |publisher=IBM Corporation |page=14 |url=http://www.bitsavers.org/pdf/ibm/360/GC20-1667-1_intro360arch.pdf |access-date=June 20, 2025}}</ref><ref>{{cite web |last1=Greiner |first1=Dan |title=IBM z/Architecture CPU Features A Historical Perspective |url=https://share.confex.com/share/117/webprogram/Handout/Session9220/IBM%20zArchitecture%20CPU%20History.pdf |website=Share.org |access-date=June 20, 2025}}</ref> A 12-bit offset allows reference to 4096 bytes from a single base. A 20-bit signed offset allows reference to ±512K. | ||
== See also == | == See also == | ||
Latest revision as of 20:41, 21 June 2025
In computing, a base address is a address serving as a reference point ("base") for other addresses.[1] Related addresses can be accessed using an addressing scheme.
Under the relative addressing scheme, to obtain an absolute address, the relevant base address is taken and an offset (aka displacement) is added to it. Under this type of scheme, the base address is the lowest-numbered address within a prescribed range, to facilitate adding related positive-valued offsets.
In IBM System/360 architecture, the base address is a 24-bit value in a general register (extended in steps to 64 bits in z/Architecture), and the offset is a 12-bit value in the instruction (extended to 20 bits in z/Architecture).[2][3] A 12-bit offset allows reference to 4096 bytes from a single base. A 20-bit signed offset allows reference to ±512K.
See also
References
<templatestyles src="Reflist/styles.css" />
Script error: No such module "Check for unknown parameters".