THIS MATERIAL WAS PRESENTED AT THE 1908 CHICAGO SPRING
DECUS MEETING IN A PANEL DISCUSSION ON SYSTEM TUNING.  THE MATERIAL
IN THE *.TXT FILES ARE COPIES OF THE OVERHEADS I USED AT
THE MEETING.
	THE TIMING MATERIAL PRESENTED IN THE SLIDES RESULTS1.TXT
AND RESULTS2.TXT ARE FOR A PDP-11/45,WITH A 300 MEGABYTE DISK DRIVE.
THE TIMING DATA IS NOT WELL QUALIFIED AND SHOULD BE USED
FOR RELATIVE COMPARISONS ONLY.  
THESE ROUTINES WERE DESIGNED TO ALLOW A FORTRAN PROGRAM TO
GET ACCESS TO THE ASSEMBLY LANGUAGE MACROS WHICH INTERFACE
TO FCS.  IT IS ASSUMED THE USER IS FAMILIAR WITH THE 
IAS/RSX-11  I/O OPERATIONS REFERENCE MANUAL.  THE USER SHOULD
READ THIS MANUAL CAREFULLY.  THE USER SHOULD ALSO PAY ATTENTION
TO THE APPENDIX IN THE BACK OF THE MANUAL WHICH DETAILS THE
CONTENTS OF THE FILE DESCRIPTOR BLOCK (FDB).
	IN USING THESE SUBROUTINES THE USER ALLOCATES A 128 BYTE
ARRAY IN HIS FORTRAN PROGRAM TO HOLD THE FDB.  THE SUBROUTINES
USE THIS ARRAY AS THEIR FDB WHEN CALLING THE FCS MACROS.
THUS THE FORTRAN PROGRAMMER HAS COMPLETE ACCESS TO EVERY 
PARAMETER THAT FCS KEEPS IN THE FILE DESCRIPTOR BLOCK.
THE FCS MACROS ALSO RETURN A VALUE TO A TWO WORD I/O STATUS BLOCK.
THE "INIT" SUBROUTINE MODIFIES THE F.BKST FIELD IN THE FDB SO THAT
THE ADDRESS OF THE I/O STATUS BLOCK POINTS TO BYTES 124-128 OF
THE FDB ARRAY.  THUS THE FORTRAN PORGRAMMER CAN EXAMINE BYTES 124-128
OF THE FDB TO SEE WHAT FCS PLACES IN THE I/O STATUS BLOCK AFTER
EACH I/O OPERATION.
	THE USER SHOULD PAY PARTICULAR ATTENTION TO THE FOLLOWING
LOCATIONS IN THE FDB.
F.RTYP	RECORD TYPE BYTE
F.RATT	RECORD ATTRIBUTE BYTE
F.RSIZ	RECORD SIZE BYTE

THE "HOW OPEN CODE" FIELD IS COMPOSED OF TWO BYTES, RACC AND FACC
THEY ARE FOUND IN THE FDB.  FOR MORE DETAIL THE USER IS  REFERRED TO 
THE FILE "HOC.DOC" IN THIS UIC.
				RESPECTIVELY SUBMITTED

				PHILIP H. CANNON
				SCIENCE APPLICATIONS, INC.
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