IBM 704

The IBM 704 was an improved version of the IBM 701. The memory was changed to magnetic core memory and three index registers were added. To support these new features, the instructionss were expanded to use the full 36 bit word. This new instruction set became the base upon which the later members of the IBM 700/7000 series expanded.

The IBM 704, the first mass-produced computer with floating point arithmetic hardware, was introduced by IBM in April, 1956. To quote the IBM 704 Manual of Operation:

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.

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.

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.

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IBM 704

Instruction Format