EXTMT.MAC IS A FORTRAN CALLABLE MAGNETIC TAPE HANDLER. IT IS CAPABLE OF READING OR WRITING TAPES IN ANY ARBITRARY FORMAT. AS HEREIN IMPLEMENTED THE TAPE DENSITY IS 800 BPI (CORE DUMP MODE FOR 7-TRACK), LATERAL PARITY IS EVEN AND THE TAPE MUST BE MOUNTED ON DRIVE #0. NO INTERRUPTS ARE USED. TO CHANGE ANY OF THESE FIXED PARAMETERS IT IS NECESSARY TO CHANGE THE COMMAND PROTOTYPE LABELED "COMAND" IN THE ASSIGNMENTS SECTION AS REQUIRED PRIOR TO ASSEMBLY OF THE SUBROUTINE. THE CONDITIONAL ASSEMBLY SWITCH "CHANGE" IS PROVIDED FOR THIS PURPOSE. COMPLETE INSTRUCTIONS ON THE FORTRAN CALLING SEQUENCE ARE PRESENTED IN A DESCRIPTION SECTION. ALSO, BOTH A SAMPLE FORTRAN PROGRAM AND USER ASSEMBLY INSTRUCTIONS ARE GIVEN.