Base address

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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

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References

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  1. ^ "What is a base address?". www.wearedevelopers.com. Retrieved 20 June 2025.
  2. ^ Student Text Introduction to IBM System/360 Architecture (PDF). IBM Corporation. April 1968. p. 14. Retrieved June 20, 2025.
  3. ^ Greiner, Dan. "IBM z/Architecture CPU Features A Historical Perspective" (PDF). Share.org. Retrieved June 20, 2025.
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