On Fri, 23 Feb 2018 14:12:37 -0800, Charles Mills wrote: >That is what I thought. How can a national grid work if SCE is zigging when >PG&E is zagging? > >-----Original Message----- >From: Jesse 1 Robinson >Sent: Friday, February 23, 2018 1:49 PM > >Long before I came to work for one, I heard that power companies are pretty >rigorous in maintaining a constant sine wave, whether 50 or 60 Hz. The power >might go out (!), but it won't wander in frequency. > But now I'm confused. The description of TIMER says: For TUINTVL, the address is a fullword containing the time interval. The time interval is presented as an unsigned 32-bit binary number; the low-order bit has a value of one timer unit (approximately 26.04166 microseconds).
That has to be right, or else programmers would have noticed. And a less official source (but agreeing with Tony) says: http://www10.dict.cc/wp_examples.php?lp_id=1&lang=en&s=interval%20timer IBM System/360 architecture If the interval timer feature is installed, the processor decrements the word at location 80 ('50'X) at regular intervals; the architecture does not specify the interval but does require that value subtracted make it appear as though 1 were subtracted from bit 23 300 times per second. But bit 23 must have 256 times the value of the low-order bit, and 26.04167 * 256 = 6666.66752 ... which is 1/150 second, not 1/300 sec. Was the interval timer the only source of time-of-day on those early models? If so, the External interrupt handler must reload its register before another tick is lost -- easy enough at power frequencies, challenging for a higner resolution interval timer. I suspect CDC 6600 had such a problem. I spotted in the source code a fudge factor, uncommented, which could most plausibly be an accommodation for missed ticks. (Or for k != ki.) -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN