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Changes from the 701 included the use of core memory (instead of Williams tubes) and addition of three index registers. To support these new features, the instructions were expanded to use the full 36-bit word. The new instruction set became the base for the IBM 700/7000 series scientific computers.
To quote the IBM 704 Manual of operation (see external links below):
IBM stated that the device was capable of executing up to 40,000 instructions per second.
123 IBM 704 systems were sold from 1955 to 1960.
The 704 left a legacy in the Lisp programming language, whose car and cdr functions take their names from 704 operations, "Contents of Address Register" and "Contents of Decrement Register", that access the two 15-bit fields of a word.
The basic instruction format was a 3-bit prefix, 15-bit decrement, 3-bit tag, and 15-bit address. The prefix field specified the class of instruction. The decrement field often contained an immediate operand to modify the results of the operation, or was used to further define the instruction type. The three bits of the tag specified three index registers, the contents of which were subtracted from the address to produce an effective address . The address field either contained an address or an immediate operand.
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