[HECnet] US DST

I agree with Dan.? I'm not aware of William's speculation being true and I strongly suspect it isn't true, although the point about time formatting might be.? I don't remember enough about parsing time to have an informed opinion on Unix. I first used Unix in the early winter of 1978 on a PDP-11/05 in WPI's CS lab where I was an operator.? A C class was being taught by an early Unix enthusiast.? We were impressed by certain things yet remained underwhelmed.? The performance was less than compelling, some of the facilities appeared primitive and the defaults for job control and editing characters weren't anything like what we were used to.? Unix was mostly never booted in favor of running RSX or RT. I don't remember any particular special handling of time or date nor do I recall the C library of the time having any support for the richness that exists today.? Given the limitations of the machines of the time, a significant portion of us couldn't understand why you wouldn't want to use assembler.? For myself, I stuck with RT-11 on a PDP-11/40 in the Mechanical Engineering lab (where I was also an operator).? The 11/40 was a far faster machine and it also had a GT40 on it.? Very nice. I don't see how the Unix on any 11 of the time (pre-11/70) would have had the storage or bandwidth to do the processing William is talking about.? A careful examination of a Bell bill of time (to see how we could reduce costs) led us to speculate that an IBM mainframe running MVS was probably being used to do the billing. That would have been one of the few systems around with the kind of capacity to handle the datasets in question. What's more likely has happened with respect to time formattong is cross-fertilization.? Operating systems have lifted ideas from each other. 1. Sun OS, Linux and Windows took the memory mapped file paradigm from TENEX/Tops-20. 2. Tab recognition for shells is right out of COMND% on Tops-20 (except all native Tops-20 programs have it). 3. Tops-20 almost, but didn't quite have pipes and didn't have relative directory specifications.? It now has pipes, but the relative directory specification needs a buff and polish. That's clearly from Unix. 4. Some good ideas have come from Multics, too. With regards to time, as far as I am aware (meaning I don't know about Multics), from its beginning, TENEX had the richest time handling.? The time was stored internally as two 18 bit half words, the left half being the elapsed dates since midnight-GMT November 17th, 1858 (this conforms with (the Smithsonian Astronomical Date Standard).? The right halfword is the number of seconds elapsed since midnight.? TENEX had a number of JSYI to both parse, convert and print time using the local timezone.? It also has a certain amount of code to handle daylight savings time and has had it since at least 1971. Tops-20 has certain improvements and minor changes.? Tops-20 has a table to account for what year is being used in order to know when the start and end of DST is (for example, double war time in WWII).? This was either written by or improved by MRC in the 1980's and allows us to handle the number of changes that happened to the legislated start and end of DST over the years (particularly during the energy crisis of the 1970's). There is an interesting incompatibility in internal formats.? It will be noted that the number of seconds in a day can be stored in 17 bits, whereas the right halfword is 18 bits.? DEC changed the internal format for the elapsed time to be the binary fraction of 1/2**18, or about 1/3 of a second.? This allows for simpler arithmetic operations, which can essentially be done on a 36 bit fixed point number.? Unfortunately, it means that, when transferring special pages between TENEX and Tops-20 using FTP, you have to format the times in ASCII.? Tops-20 will run out of time on 7-Aug-2576 19:59:59, a sad day indeed. Having nicer time output just seems like a logical progression of nice ideas.? It's hard to tell where Unix got it from.? I think it probably showed up in the C library first, but I don't know why. It could have been from Tops-20, but maybe VMS beat Unix to the punch and Unix got it from there.? There was a certain amount of cross-fertilization between Ultrix and Tops-20, less so between VMS and Tops-20, which is unfortunate.