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Under MIB addressing, the base and displacement are used to compute an effective address as base + displacement. [ 1 ] : §3.1.1.3 The register specified by the SIB byte's INDEX field does not participate in this effective-address calculation, but is instead treated as a separate input argument to the instructions using this addressing mode.
In computer engineering and low-level programming (such as assembly language), an offset usually denotes the number of address locations added to a base address in order to get to a specific absolute address. In this (original) meaning of offset, only the basic address unit, usually the 8-bit byte, is used to
In computing, a base address is an address serving as a reference point ("base") for other addresses. 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.
Any of the addressing modes mentioned in this article could have an extra bit to indicate indirect addressing, i.e. the address calculated using some mode is in fact the address of a location (typically a complete word) which contains the actual effective address. Indirect addressing may be used for code or data.
Direct address: ADD.A address 1 — add the value stored at address 1; Memory indirect: ADD.M address 1 — read the value in address 1, use that value as another address and add that value; Many ISAs also have registers that can be used for addressing as well as math tasks. This can be used in a one-address format if a single address register ...
This allows each half of a user's address space to be limited to a set section of main memory, designated by the base physical address and size. This allows the model of separate read-only shareable code segment (normally the high segment) and read-write data/stack segment (normally the low segment) used by TOPS-10 and later adopted by Unix.
The invention of dynamic address translation (the function provided by an MMU) originally reduced the need for position-independent code because every process could have its own independent address space (range of addresses). However, multiple simultaneous jobs using the same code created a waste of physical memory.
In the case of the NOP instruction, the second value in the second byte is the "base" register of a combined base register, displacement register and offset address. If the base register is also 0, the branch is not taken regardless of the value of the displacement register or displacement address. NOPR: 2