History
Index registers, commonly known as a B-line in early British computers, were first used in the British Manchester Mark 1 computer, in 1949. In general, index registers became a standard part of computers during the technology's second generation, (roughly 1954–1966) Machines in the IBM 700/7000 mainframe series had them, starting with the IBM 704 in 1954, though they were optional on some smaller machines such as the IBM 650 and IBM 1401.
Early "small machines" with index registers include the AN/USQ-17, around 1960, and the real-time computers from Scientific Data Systems. The first microprocessor with a true index register appears to have been the Motorola 6800, whose upgraded clone MOS Technology 6502 made good use of two such registers. (The earlier Intel 8080 did allow indirect addressing via a register.)
Modern computer designs generally do not include dedicated index registers; instead they allow any general purpose register to contain an address, and allow a constant value and, on some machines, the contents of another register to be added to it as an offset to form the effective address. Early computers designed this way include the PDP-6 and the IBM System/360.
Read more about this topic: Index Register
Famous quotes containing the word history:
“There is one great fact, characteristic of this our nineteenth century, a fact which no party dares deny. On the one hand, there have started into life industrial and scientific forces which no epoch of former human history had ever suspected. On the other hand, there exist symptoms of decay, far surpassing the horrors recorded of the latter times of the Roman empire. In our days everything seems pregnant with its contrary.”
—Karl Marx (1818–1883)
“I cannot be much pleased without an appearance of truth; at least of possibility—I wish the history to be natural though the sentiments are refined; and the characters to be probable, though their behaviour is excelling.”
—Frances Burney (1752–1840)
“This above all makes history useful and desirable: it unfolds before our eyes a glorious record of exemplary actions.”
—Titus Livius (Livy)