IBM 7090

The IBM 7090 a second-generation transistorized version of the earlier IBM 709 vacuum tube mainframe computers and was designed for "large-scale scientific and technological applications", was the third member of the IBM 700/7000 series. The first 7090 installation was in November 1959.

The 7090 used a 36-bit "word", with an address-space of 32K (32,768) words. It operated with a basic clock cycle of 2.18 μs.

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.