The IBM 650 (photo) was one of IBM’s early computers, and the world’s first mass-produced (photo) computer. It was announced in 1953, and over 2000 systems were produced between the first shipment in 1954 and its final manufacture in 1962. Support for the 650 and its component units was withdrawn in 1969.
The 650 is a two-address, bi-quinary coded decimal machine (both data and addresses were decimal), with memory on a rotating drum. The 650 was specifically designed for users of existing IBM unit record equipment (electro-mechanical punched card-processing machines) upgrading from so-called Calculating Punches, like the IBM 604 model, to computers proper.
The basic 650 system consisted of three components:
The rotating drum memory (photo) provided 2,000 signed 10-digit words of memory (5 character per word) at addresses 0000 to 1999. A word could not be accessed until its location on the drum surface passed under the read/write heads during rotation (rotating at 12,500 rpm, the non-optimized average access time was 2.5 ms). Because of this timing restriction, the second address in each instruction word was the address of the next instruction. Programs could be optimized by placing instructions around the drum based on the expected execution time of the previous instruction. One specialized instruction, 'Table lookup', could high-equal compare a reference 10 digit word with 46 consecutive following words on the drum in one 5ms revolution and then switch to the next track in time for the next 46 words (there were fifty words per track/revolution). This feat was only three times slower than on a one-thousand times faster binary machine in 1963 (1500 microsecs on the IBM7040 to 5000 microsecs on the IBM650 for looking up 46 entries as long as both were programmed in assembler. One higher level language made the IBM7040 dramatically slower at table-look-up. An upgraded 4,000 word drum became available in 1959.
The optional Auxiliary Unit (IBM 653), was introduced on May 3, 1955, providing up to three features:
The IBM 533 reader punch unit could only read a maximum of 26 columns of alphnumerics from cards in mostly fixed columns. An expansion allowed more but certainly not over 50, as only ten words could be read from a card (5 characters per word).
The IBM 650 (pictured here) at the Haus zur Geschichte der IBM Datenverarbeitung (House for the History of IBM Data Processing), Sindelfingen, is still running (as of May 2004) and will process an income tax program of the time, with input and output on punched cards.
The IBM 7070, announced 1960, was designed to provide a "transistorized IBM 650" upgrade path. The IBM 1620, introduced in 1959, addressed the lower end of the market. Both were decimal machines, but neither were instruction set compatible.