THE "HOW OPEN CODE" FIELD IS COMPOSED OF TWO BYTES, RACC AND FACC
THE LOW ORDER BYTE IS THE FACC (FILE ACCESS BYTE)
AND THE HIGH ORDER BYTE IS THE RACC (RECORD ACCESS BYTE).
THEY ARE FOUND IN THE FDB.

F.RACC	RECORD ACCESS BYTE.  BIT 0 THROUGH 3 OF THIS BYTE DEFINE
	THE RECORD-ACCESS MODES.

	BIT 0 =1 TO INDICATE READ$/WRITE$ MODE (FD.RWM); OTHERWISE
	IT IS 0 TO INDICATE GET$/PUT$ MODE
	
	BIT 1 = 1 TO INDICATE RANDOM-ACCESS MODE (FD.RAN) FOR GET$/PUT$
	RECORD I/O;  OTHERWISE, IT IS 0 TO INDICATE SEQUENTIAL ACCESS
	MODE.

	BIT 2 = 1 TO INDICATE LOACATE MODE (FD.PLC) FOR GET$/PUT$
	RECORD I/O; OTHERWISE, IT IS 0 TO INDICATE MOVE MODE.

	BIT 3 = 1 TO INDICATE THAT PUT$ OPERATION IN SEQUENTIAL MODE
	DOES NOT TRUNCATE THE FIELD (FD.INS); OTHERWISE, IT IS 0
	TO INDICATE THAT PUT$ OPERATION IN SEQUENTIAL MODE TRUNCATES
	THE FILE.

F.FACC	FILE-ACCESS BYTE.  THIS BYTE INDICATES THE ACCESS PRIVILEGES
	FOR A FILE.

	BIT 0 = 1 IF THE FILE IS ACCESSED FOR READ ONLY (FA.RD).
	
	BIT 1 = 1 IF THE FILE IS ACCESSED FOR WRITING (FA.WRT).

	BIT 2 = 1 IF THE FILE IS ACCESSED FOR EXTENDING (FA.EXT).

	BIT 3 = 1 IF A NEW FILE IS BEING CREATED (FA.CRE); OTHERWISE
	IT IS 0 TO INDICATE AN EXISTING FILE.

	BIT 4 =1 IF THE FILE IS A TEMPORARY FILE (FA.TMP).

	BIT 5 = 1 IF THE FILE IS OPENED FOR SHARED ACCESS (FA.SHR).

	IF BIT 3 ABOVE IS 0;

	BIT 6 = 1 IF AN EXISTING FILE IS BEING APPENDED (FA.APD).

	IF BIT 3 ABOVE IS 1;

	BIT 6 = 1 IF NOT SUPERSEDING AN EXISTING FILE AT FILE-
	CREATE TIME (FA.NSP).

SOME TYPICAL VALUES FOR THE "HOW OPEN CODE" (HOC) ARE AS FOLLOWS:
 
 
ALL VALUES FOR THE HOC ARE IN OCTAL
 
 
HOC = 416	FILE IS ACCESSED FOR WRITE
		FILE IS ACCESSED FOR EXTENDING
		A NEW FILE WILL BE CREATED
		
		FILE WILL BE ACCESSED USING DIRECT ACCESS
		(RANDOM) BLOCK I/O.
HOC = 402	FILE IS ACCESSED FOR WRITE
		
		FILE WILL BE ACCESSED USING DIRECT ACCESS
		(RANDOM) BLOCK I/O.
HOC = 401	FILE IS ACCESSED FOR READ ONLY

		FILE WILL BE ACCESSED USING DIRECT ACCESS
		(RANDOM) BLOCK I/O.
HOC = 516	FILE IS ACCESSED FOR WRITE
		FILE IS ACCESSED FOR EXTENDING
		IF THE FILE EXISTS IT WILL BE SUPERSEEDED
		(OVERWRITTEN), IF THE FILE DOES NOT
		EXIST IT WILL BE CREATED.
		FILE WILL BE ACCESSED USING DIRECT ACCESS
		(RANDOM) BLOCK I/O.
HOC = 441	FILE IS ACCESSED FOR READ ONLY
		FILE IS OPENED FOR SHARED ACCESS

		FILE WILL BE ACCESSED USING DIRECT ACCESS
		(RANDOM) BLOCK I/O.



RECORD I/O



HOC = 1016	FILE IS ACCESSED FOR WRITE
		FILE IS ACCESSED FOR EXTENDING
		A NEW FILE WILL BE CREATED

		FILE WILL BE ACCESSED USING RANDOM 

		ACCESS OF FIXED LENGTH RECORDS.  BUFFERING
		OF THE RECORDS WILL TAKE PLACE.
THE FORTRAN OFFSETS FOR INTEGER*2 ARRAY OF SOME
IMPORTANT LOCATIONS IN THE FDB.
 
 
 
F.FNB=FDB(34)
F.ERR=FDB(22)
F.CNTG=FDB(15)
N.FID=FDB(34)
F.VERR=FDB(41)
N.DVNM=FDB(47)
N.UNIT=FDB(48)



F.VERR	IS THE VERSION NUMBER OF THE FILE YOU HAVE OPENED


INFORMATION ON THE CONTENTS OF THE F.ERR, F.ERR+1
ERROR WORD


F.ERR	NEGATIVE IMPLIES AN ERROR
F.ERR+1 IF F.ERR IS NEGATIVE, THEN
	F.ERR+1 =0 IMPLIES AN I/O ERROR CODE IN F.ERR
	F.ERR+1 <0 IMPLIES A DIRECTIVE ERROR CODE IN F.ERR

NOTES ON THE F.CNTG WORD

F.CNTG = 0 LEAVE THE FILE EMPTY
F.CNTG < 0 ALLOCATE THE NUMBER OF BLOCKS NONCONTIGUOUS
	AND LEAVE THE FILE NONCONTIGUOUS
F.CNTG > 0 ALLOCATE THE NUMBER OF BLOCKS CONTIGUOUS AND
	LEAVE THE FILE CONTIGUOUS.

NOTES ON OPEN BY FILE ID

ONE MUST SPECIFY AT LEAST THE
N.FID (34) FILE NUMBER
	(35) FILE SEQUENCE NUMBER
	(36) 0 (RESERVED)
N.DVNM (47) TWO LETTER ASCII DEVICE NAME
N.UNIT (48) BINARY VALUE OF THE DEVICE UNIT NUMBER
		FILE WILL BE ACCESSED USING DIRECT ACCESS
		(RANDOM) BLOCK I/O.


SPACE SAVING TIPS


IF YOU USE DIRECT ACCESS BLOCK I/O ONE DOES
NOT NEED ANY SPACE IN THE FSR1 BUFFER OR IN THE
$DEVT TABLE.  THUS YOU CAN SET ACTFIL=0 AND UNITS=0
EVEN THOUGHT YOU HAVE ACTIVE FILES AND UNITS.  THE
UNITS= N IS TO MAKE FORTRAN RESERVE SPACE FOR
FDBS AND THE ACTFIL IS FOR FORTRAN TO RESERVE SPACE
TO DE-BLOCK A FILE.  WHEN YOU DO DIRECT ACCESS THE
DISK TRANSFERS DIRECTLY INTO YOUR ARRAY.  THERE IS
NO NEED TO SUPPLY A BUFFER FOR DE-BLOCKING.
YOU HAVE ALREADY SUPPLIED THE FDB IN AN ARRAY IN
YOUR FORTRAN PROGRAM.



INFORMATION ON RECORD I/O 


LOCATIONS IN THE FDB


F.RTYP	RECORD-TYPE BYTE.   THIS BYTE IS SET AS FOLLOWS
	TO INDICATE THE TYPE OF RECORDS FOR THE FILE:

	F.RTYP=1 IMPLIES FIXED-LENGTH RECORDS (R.FIX)
	F.RTYP=2 IMPLIES VARIABLE-LENGTH RECORDS (R.VAR)
	F.RTYP=3 IMPLIES SEQUENCED RECORDS (R.SEQ)

F.RATT	RECORD-ATTRIBUTE BYTE.  

	BIT 0 - IF SET TO A 1, IT IMPLIES THAT THE FIRST BYTE
		OF A RECORD IS TO CONTAIN A FORTRAN CARRIAGE-
		CONTROL CHARACTER (FD.FTN)
	BIT 1 - IF SET TO A 1, IT IMPLIES THAT FOR A CARRIAGE-
		CONTROL DEVICE THAT A LINE FEED IS TO BE PERFORMED
		BEFORE THE LINE IS PRINTED AND A CARRIAGE RETURN IS 
		TO BE PERFORMED AFTER THE LINE IS PRINTED (FD.CR).
	BIT 2 - NOT USED
	BIT 3 - IF SET TO A 1, IT IMPLIES THAT RECORDS CANNOT CROSS
		BLOCK BOUNDARIES (FD.BLK).


F.RSIZ	RECORD-SIZE WORD.  THIS WORD CONTAINS THE SIZE OF FIXED-LENGTH
	RECORDS (IN BYTES) OR INDICATES THE SIZE OF THE LARGEST RECORD
	THAT CURRENTLY EXISTS IN A FILE OF VARIABLE-LENGTH RECORDS.


THE LOCATIONS OF THESE BYTES IN THE FDB IS AS FOLLOWS

THE RECORTD TYPE BYTE IS THE FIRST BYTE IN THE FDB
THE RECORD ATTRIBUTE BYTE IS THE SECOND BYTE IN THE
FDB
F.RATT,F.RTYP=FDB(1)

THE RECORD SIZE WORD IS THE SECOND WORD IN THE FDB
F.RSIZ=FDB(2)
WHEN YOU ARE CREATING A NEW FILE 
THESE TWO WORDS MUST BE FILLED IN AFTER INIT AND 
BEFORE A FILE IS OPENED.

IF THE FILE EXIST, THEY WILL BE FILLED IN BY
THE OPEN COMMAND