Changes from the 701 included the use of magnetic core memory 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 later members of the IBM 700/7000 series.

To quote the IBM 704 Manual of operation (see external link below):

The type 704 Electronic Data-Processing Machine is a large-scale,

high-speed electronic calculator controlled by an internally stored

program of the single address type.

123 IBM 704 systems were sold from 1955 to 1960.

Instruction format

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.

External links