IBM 709

The IBM 709 is a discontinued computer system introduced by IBM in August 1958. It is an improved version of the IBM 704 and the second member of the IBM 700/7000 series of scientific computers. The improvements included overlapped input/output, indirect addressing, and three "convert" instructions which provided support for decimal arithmetic, leading zero suppression, and several other operations. The 709 had 32,768 words of 36-bit magnetic core memory and could execute 42,000 add or subtract instructions per second. It could multiply two 36-bit integers at a rate of 5000 per second.

An optional hardware emulator executed legacy IBM 704 programs on the IBM 709. This was the first commercially available emulator prior to 1960. Registers and most 704 instructions were emulated in 709 hardware. Complex 704 instructions such as floating point trap and input-output routines were emulated in 709 software.

The FORTRAN Assembly Program was first introduced for the 709.

It was a large system; customer installations used 100 to 250 kW to run them and almost as much again on the cooling. The 709 was built using vacuum tubes.

IBM introduced a transistorized version of the 709, called the IBM 7090, in November 1959.

The IBM 709 has a 38-bit accumulator, a 36-bit multiplier quotient register, and three 15-bit index registers whose contents are subtracted from the base address instead of being added to it. All three index registers can participate in an instruction: the 3-bit tag field in the instruction is a bit map specifying which of the registers participate in the operation, however if more than one index register is specified, their contents are combined by a logical or operation, not addition.^p. 12

There are five instruction formats, referred to as Types A, B,C, D and E. Most instructions are of type B.

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