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A pair of a word address and an offset within the word is called a wide address (also known as a fat address or fat pointer). (This should not be confused with other uses of wide addresses for storing other kinds of supplemental data, such as the bounds of an array.) The stored offset may be either a bit offset or a byte offset.
An eight-bit processor like the Intel 8008 addresses eight bits, but as this is the full width of the accumulator and other registers, this could be considered either byte-addressable or word-addressable. 32-bit x86 processors, which address memory in 8-bit units but have 32-bit general-purpose registers and can operate on 32-bit items with a ...
Alternatively many word-oriented machines implement byte operations with instructions using special byte pointers in registers or memory. For example, the PDP-10 byte pointer contained the size of the byte in bits (allowing different-sized bytes to be accessed), the bit position of the byte within the word, and the word address of the data ...
On most systems, the address of a multi-byte simple data value is the address of its first byte (the byte with the lowest address). There are exceptions to this rule – for example, the Add instruction of the IBM 1401 addresses variable-length fields at their low-order (highest-addressed) position with their lengths being defined by a word ...
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. Intel 80386) addresses 2 32 (4,294,967,296) locations, or a 4 GiB address space. In contrast, a 36-bit word-addressable machine with an 18-bit address bus ...
A one-word sequence descriptor in memory, called a "byte pointer", held the current word address within the sequence, a bit position within a word, and the size of each byte. Instructions existed to load and store bytes via this descriptor, and to increment the descriptor to point at the next byte (bytes were not split across word boundaries).
A processor with 128-bit byte addressing could directly address up to 2 128 (over 3.40 × 10 38) bytes, which would greatly exceed the total data captured, created, or replicated on Earth as of 2018, which has been estimated to be around 33 zettabytes (over 2 74 bytes). [1] A 128-bit register can store 2 128 (over 3.40 × 10 38) different values.
Also, 12-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, address buses, or data buses of that size. Before the widespread adoption of ASCII in the late 1960s, six-bit character codes were common and a 12-bit word, which could hold two characters, was a convenient size. This ...