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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.
A computer program can access an address given explicitly – in low-level programming this is usually called an absolute address, or sometimes a specific address, and is known as pointer data type in higher-level languages. But a program can also use relative address which specifies a location in relation to somewhere else (the base address).
An odd offset would cause a program check (unless the base register itself also contained an odd address)—since instructions had to be aligned on half-word boundaries to execute without a program or hardware interrupt. The previous example describes an indirect way to address to a memory location in the format of segment:offset.
In logical block addressing, only one number is used to address data, and each linear base address describes a single block. The LBA scheme replaces earlier schemes which exposed the physical details of the storage device to the software of the operating system. Chief among these was the cylinder-head-sector (CHS) scheme, where blocks were addressed by means
The segment address is always added to a 16-bit offset in the instruction to yield a linear address, which is the same as physical address in this mode. For instance, the segmented address 06EFh:1234h (here the suffix "h" means hexadecimal ) has a segment selector of 06EFh, representing a segment address of 06EF0h, to which the offset is added ...
Addressing modes are an aspect of the instruction set architecture in most central processing unit (CPU) designs. The various addressing modes that are defined in a given instruction set architecture define how the machine language instructions in that architecture identify the operand(s) of each instruction.
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When writing to memory, the CPU writes data from MDR to the memory location whose address is stored in MAR. MAR, which is found inside the CPU, goes either to the RAM (random-access memory) or cache. The MAR register is half of a minimal interface between a microprogram and computer storage; the other half is a MDR.