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C00002 00002	Date75 advisory updated 22 Nov.
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Date75 advisory updated 22 Nov.

January 4, 1975 is the last date representable in the old PDP-6 format
date field.  The following changes have been implemented to extend the
dates for an additional 77 years.

1. DATE UUO [CALLI 14]
	returns a 15 bit date, instead of 12 bits as previously documented.

2. Disk file dates
	LOOKUP and RENAME have been changed to use bits 18-20 of
	the second (extension) word of the argument block as the high bits
	of the date last written.  The low bits of the date last written
	are bits 24-35 of the third word.

3. Dectapes (PDP-6 format)
	LOOKUP returns the date in bits 24-35 of the third word
	and bits 18-20 of the second word.
	RENAME accepts a date in the same format.
	ENTER ignores the date entirely; files always get their
	date set to the current date by ENTER.

	Note that the 15-bit date will actually be stored in bits
	21-35 of the third word of the directory entry, and the split
	field in LOOKUP and RENAME arguments is only for compatability
	with the disk UUOs.  Note that people who try to interpret the
	data returned by LOOKUP should avoid being confused by the high
	order date field which is returned in (bits 18-20 of) the halfword
	which formerly contained only the first block number of the file (now
	confined to bits 21-35).

	ENTER, by the way, returns the block number of the first block of
	the file in bits 21-35 of the second word.

4. Dectapes (PDP-10 format)
	The extra date bits are smeared in the extra bit of the slot words.
	The format is too horrible to explain here, see REG if you really
	want to know.  This affects only user programs since pdp-10 dectapes
	are not supported by the system.  The programs 	6TO10, 10TO6, and
	DMAN are NOT supported and will be not be converted.  TENDMP will
	be supported for PDP-10 dectape manipulation.

5. ACCTIM works as before.

6. DSKTIM has no provision for a 15 bit date.  DSKTIM will be withdrawn from
	service before Jan 5.

Conversion of programs to DATE75.

The following rules should be followed:

	ENTER
	The only date field that's relevant is the creation date in bits
	21-35 of the extension word (disk only).  If you wish to set the
	creation date use this field, otherwise zero it.

	LOOKUP
	works as before; if you want to print the file's date last written
	you must get that date from two words returned by LOOKUP.

	RENAME
	To get the default date and time, zero bits 9-35 in the third word, and
	bits 18-20 in the second word.  Otherwise, set these fields explicitly.