page_title: IBM 700/7000 series
section_title: Later scientific architecture (704/709/7090/7094)
hierarchical_section_title: IBM 700/7000 series / Later scientific architecture (704/709/7090/7094)
caption_attribution_description: English: NASA mission control computer room with dual IBM 7090's, apparently taken around the time of the Mercury Atlas 6 (MA-6) mission in 1962. From US National Archives and Record Administration ARC system. Creator: National Aeronautics and Space Administration. (10/01/1958 - ) ( Most Recent) Type of Archival Materials: Photographs and other Graphic Materials Level of Description: Item from Record Group 255: Records of the National Aeronautics and Space Administration, 1903 - 1988 Location:NARA's Southwest Region (Fort Worth) (NRFFA), 501 West Felix Street, Building 1, Fort Worth, TX 76115-3405 PHONE: 817-831-5620, FAX: 817-334-5621, EMAIL: ftworth.archives@nara.gov Part of: File Unit: MA - 6 Photo -- CCK's Personal Copy (w:Christopher C. Kraft), Scope &amp; Content Note: This is a photograph of a computer room at NASA. Access Restrictions: Unrestricted Use Restrictions: Unrestricted Specific Records Type:scientific illustration Variant Control Number(s): NAIL Control Number: NRFF-255-70-37(6)-CCK1
context_page_description: The IBM 700/7000 series is a series of large-scale computer systems that were made by IBM through the 1950s and early 1960s. The series includes several different, incompatible processor architectures. The 700s use vacuum-tube logic and were made obsolete by the introduction of the transistorized 7000s. The 7000s, in turn, were eventually replaced with System/360, which was announced in 1964. However the 360/65, the first 360 powerful enough to replace 7000s, did not become available until November 1965. Early problems with OS/360 and the high cost of converting software kept many 7000s in service for years afterward.
context_section_description: IBM's 36-bit scientific architecture was used for a variety of computation-intensive applications. First machines were the vacuum-tube 704 and 709, followed by the transistorized 7090, 7094, 7094-II, and the lower-cost 7040 and 7044. The ultimate model was the Direct Coupled System (DCS) consisting of a 7094 linked to a 7044 that handled input and output operations.
  Data formats
  Numbers are 36 bits long, both fixed point and floating point. (See: Why 36 bits?)
  Fixed-point numbers are stored in binary sign/magnitude format.
  Single-precision floating-point numbers have a magnitude sign, an 8-bit excess-128 exponent and a 27-bit magnitude
  Double-precision floating-point numbers, introduced on the 7094, have a magnitude sign, a 17-bit excess-65536 exponent, and a 54-bit magnitude
  Alphameric  characters are 6-bit BCD, packed six to a word.
  Instruction format
  The basic instruction format is a three-bit prefix, fifteen-bit decrement, three-bit tag, and fifteen-bit address. The prefix field specifies the class of instruction. The decrement field often contains an immediate operand to modify the results of the operation, or is used to further define the instruction type. The three bits of the tag specify three (seven in the 7094) index registers, the contents of which are subtracted from the address to produce an effective address. The address field either contains an address or an immediate operand.
  Registers
  Processor registers consisted of:
  AC  – 38-bit Accumulator
  MQ – 36-bit Multiplier-Quotient
  XR  – 15-bit Index Registers (three or seven)
  SI    – 36-bit Sense Indicator
  The accumulator (and multiplier-quotient) registers operate in sign/magnitude format.
  The Index registers operate using two's complement format and when used to modify an instruction address are subtracted from the address in the instruction. On machines with three index registers, if the tag has two or three bits set (i.e. selected multiple registers) then their values are ORed together before being subtracted. The IBM 7094, with seven index registers has a "compatibility" mode to permit programs from earlier machines that used this trick to continue to be used.
  The Sense Indicators permit interaction with the operator via panel switches and lights.
  Memory
  704: 4,096 or 8,192 or 32,768 – 36-bit binary words with six-bit characters
  709, 7090, 7094, 7094 II, 7040, 7044: 32,768 – 36-bit binary words with six-bit characters
  Input/output
  The 709/7090 series use Data Synchronizer Channels for high speed input/output, such as tape and disk. The basic 7-bit DSCs, e.g., 7607, execute their own simple programs from the computer memory that controls the transfer of data between memory and the I/O devices; the more advanced 9-bit 7909 supports more sophisticated channel programs. Because the unit record equipment on the 709x was so slow, Punched card I/O and high-speed printing were often performed by transferring magnetic tapes to and from an off-line IBM 1401. Later, the data channels were used to connect a 7090 to a 7040 or a 7094 to a 7044 to form the IBM 7094/7044 Direct Coupled System (DCS). In that configuration, the 7044, which could use faster 1400 series peripherals, primarily handled I/O.
caption: IBM 7090's at NASA's Project Mercury, 1962
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