Byte addressing in hardware architectures supports accessing individual bytes. Computers with byte addressing are sometimes called byte machines, in contrast to word-addressable architectures, word machines, that access data by word. Programs took advantage of this flexibility: those not needing lowercase letters used the limited character set of 6-bit bytes for efficiency; most used 7-bit ASCII, packed 5 to a word with one unused bit; and the C implementation used 9-bit bytes because C requires all memory to be byte-addressable.
On the GE/Honeywell machines, special indirect addressing modes could be used on most instruction types, and operated on a byte pointer which could operate on either 6-bit or 9-bit bytes.
Neither of these machines originally had direct machine support for random access to bytes; adjusting a byte pointer to point N bytes before or after the byte to which it currently pointed required a sequence of multiple instructions. The KL10 PDP-10 model extended the (increment byte pointer) instruction to become the adjust byte pointer instruction, , that could adjust a byte pointer by an arbitrary number of bytes; providing a primitive for indexing into an array of bytes.
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