Source : Free On-Line Dictionary of Computing

IBM 709
     
         A computer made by {IBM} oriented toward
        scientific work.  The 709 had the same basic architecture as
        the {IBM 704} but with many {I/O} and performance refinements
        over the 704.
     
        The IBM 709 (like the 704) had 36-bit memory words, 15-bit
        addresses and instructions with one address.  A few {index
        register} instructions had the infamous 15-bit decrement field
        in addition to the 15-bit address.
     
        The {IBM 7090} was a transistorised version of the 709.
     
        [Difference between 704 and 709?]
     
        (1999-01-19)