IBM 709
| Company type | Computer system |
|---|---|
| Industry | Computing |
| Predecessor | IBM 704 |
| Founded | January 1957 |
| Successor | IBM 7090 |
| Products | Scientific computer system |
| Parent | IBM |
The IBM 709 was a computer system introduced by IBM in January 1957 and became operational in August 1958. As an upgraded model of the IBM 704, it represented the third installment in the IBM 700/7000 series tailored for scientific computing. Enhancements included overlapped input/output processing, indirect addressing capabilities, and three specialized "convert" instructions that facilitated decimal calculations, leading zero suppression, among other functions. The system was equipped with 32,768 words of 36-bit magnetic-core memory and could perform 42,000 addition or subtraction operations per second, while multiplication of two 36-bit integers was achievable at a rate of 5,000 per second.
An optional hardware emulator enabled the IBM 709 to run programs originally designed for the IBM 704—marking the first commercially available emulator. This emulator replicated registers and most instructions through hardware, delegating more complex operations to software routines.
The IBM 709 also saw the debut of the FORTRAN Assembly Program.
This substantial machine demanded between 100 and 250 kW of power for functioning, with nearly equivalent energy required for cooling systems. It weighed approximately , not including peripheral devices. The construction relied on vacuum tube technology.
In 1958, just one year after its release, IBM announced the transistor-based successor, the IBM 7090, which consequently shortened the IBM 709’s tenure in the market.
Registers
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The architecture of the IBM 709 includes a 38-bit accumulator alongside a multiplier/quotient register of 36 bits and three index registers each measuring 15 bits. Contrary to conventional designs, these index registers function by subtracting their values from the base address. The instruction format incorporates a three-bit tag field that determines which index registers are involved, combining multiple selected registers through a logical OR operation rather than summation.
Instruction and Data Formats
The instruction set is divided into five categories: Types A, B, C, D, and E, with the majority of instructions classified as type B.
Type A instructions are composed of a 3-bit prefix (instruction code), a 15-bit decrement portion, a 3-bit tag segment, and a 15-bit address field. These instructions execute conditional jumps based on decrement registers identified by the tag and may also subtract the decrement value from index registers. Due to design limitations, there are six type A instructions; one of these (STR) was introduced later with the IBM 709.
Type B instructions feature a 12-bit instruction code—distinguished by specific bits to separate them from type A—alongside a 2-bit flag field, four unused bits, a 3-bit tag, and a 15-bit address field.
Types C, D, and E cater to more specialized operational roles.
Data formats supported include:
- Fixed-point binary numbers using sign/magnitude representation.
- Single-precision floating-point numbers consisting of a sign bit, an 8-bit excess-128 exponent, and a 27-bit fraction without an implicit leading bit.
- Alphanumeric data encoded in 6-bit BCD format, allowing six characters to be packed into one word.
The instruction architecture segments data into prefix, decrement, tag, and address fields, with specific instructions designed to alter each field independently.
I/O Channel
Enhancing the capabilities of the IBM 704, the IBM 709 incorporated increased magnetic-core memory along with independent input/output channels managed by the IBM-766 data synchronizer. Unlike the IBM 704’s programmed I/O—which moved data word-by-word through the CPU—the IBM 709 could operate up to three Data Synchronizers controlling as many as 20 IBM 729 tape drives plus one each of an IBM 716 line printer, IBM 711 card reader, and IBM 721 card punch. This arrangement expanded I/O device support sixfold and enabled concurrent I/O processing alongside program execution.
Furthermore, the system allowed attachment of up to two IBM 733 Magnetic Drum units independently, each offering storage for 8,192 words. Booting options included cards, tapes, or drums.
The IBM 738 Magnetic Core Storage represented a technological hybrid by combining vacuum tube drivers with early transistor-based read sense amplifiers.
See also
- List of vacuum tube computers
- IBM 740 CRT recorder
- SHARE Operating System (SOS)
- SQUOZE
Further reading
External links
- 709 Data Processing System – IBM historical overview
- IBM 709 Data Processing System – BRL report featuring installation information and photographs
- IBM 709 page at Columbia University – includes photographic documentation