-----Original Message----- From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of John McKown Sent: Monday, January 05, 2009 4:09 PM To: IBM-MAIN@bama.ua.edu Subject: Re: the Z/10 and timers.
<SNIP> Now, I somewhat understand why. Timing on the z/OS platform is a critical resource. On Windows and Linux, it is a bit of "ah, who cares?". z/OS will die if a clock runs backwards. This is so ingrained in the software that I doubt it can every be "fixed". Not so on any other platform that I'm aware of. <SNIP> It ain't broken. Way back when, one of the things that made most of us not trust any data that came from a system that did not have a "hard clock" was that anyone could reset the time and date. If you remember correctly, the autoexec.bat file had TIME & DATE commands in it so that DOS would not ask you for the date and time when you booted the system. And this was a carry over from CP/M's lack of a need for a stable TOD. While working in Silicon Valley in the '90s, I had someone tell me that mainframes can't operate in a tightly coupled environment (and they weren't joking -- the poor guy who said this worked in Milpitas with a company that was trying to get 2 80386 CPUs to work together on the same motherboard). I looked at him and said that the S/370 had machines with 2 CPUs sharing 16MB of memory, besides having as many as 32 I/O ONLY CPUs operating on that same memory. And then there were the complexes that had 8 of these machines tied to each other. The look of astonishment was priceless. The point to this is, all of those mainframe systems lived or died based on them being in synchronization. And you can't have a clock running backwards -- that would get a Machine Check for failed timing facility. I don't think Intel, AMD or Motorola (a la 6800 or 68000 chips from when I worked with them) has an equivalent. Time only goes forward by definition (look at the Principles of Operation). This is why time change on a mainframe (S/360-30 & beyond?) took pushing a button (or flipping a switch) before you could change the TOD. You were being required to do this as an on purpose thing, not an accident with someone playing around with the time commands or instructions. Regards, Steve Thompson -- Opinions expressed by this poster are not necessarily those of poster's employer and should not necessarily be construed as such. -- ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
