square tape

from The Free On-line Dictionary of Computing (8 July 2008)

square tape

   <storage> {Mainframe} magnetic tape cartridges for use with
   {IBM 3480} or compatible tape drives; or {QIC} tapes used on
   {workstations} and {microcomputers}.  The term comes from the
   square (actually rectangular) shape of the cartridges;
   contrast {round tape}.

   [{Jargon File}]