Source : Free On-Line Dictionary of Computing

DECtape
     
         A reel of {magnetic tape} about 4 inches
        in diameter and one inch wide.  Unlike today's {macrotapes},
        microtape drivers allowed {random access} to the data, and
        therefore could be used to support {file systems} and even for
        {swapping} (this was generally done purely for {hack value},
        as they were far too slow for practical use).  DECtape was a
        variant on {LINCtape}.
     
        In their heyday DECtapes were used in pretty much the same
        ways one would now use a {floppy disk}: as a small, portable
        way to save and transport files and programs.
     
        (1995-03-16)