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This allowed a 16-bit address register, which would normally be able to access 64 KB of memory space, to access 1 MB of memory space. This segmenting of the memory space into discrete blocks with specific tasks carried over into the programming languages of the day and the concept is still widely in use within modern programming languages.
A pointer a pointing to the memory address associated with a variable b, i.e., a contains the memory address 1008 of the variable b.In this diagram, the computing architecture uses the same address space and data primitive for both pointers and non-pointers; this need not be the case.
In a system using segmentation, computer memory addresses consist of a segment id and an offset within the segment. [3] A hardware memory management unit (MMU) is responsible for translating the segment and offset into a physical address, and for performing checks to make sure the translation can be done and that the reference to that segment and offset is permitted.
A memory address a is said to be n-byte aligned when a is a multiple of n (where n is a power of 2). In this context, a byte is the smallest unit of memory access, i.e. each memory address specifies a different byte. An n-byte aligned address would have a minimum of log 2 (n) least-significant zeros when expressed in binary.
The range of addressing of memory depends on the bit size of the bus used for addresses – the more bits used, the more addresses are available to the computer. For example, an 8-bit-byte-addressable machine with a 20-bit address bus (e.g. Intel 8086 ) can address 2 20 (1,048,576) memory locations, or one MiB of memory, while a 32-bit bus (e.g ...
The memory model concept derives from the setup of the segment registers. For example, in the tiny model CS=DS=SS, that is the program's code, data, and stack are all contained within a single 64 KB segment. In the small memory model DS=SS, so both data and stack reside in the same segment; CS points to a different code segment of up to 64 KB.
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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 ...