Point taken.

What would you call the units of the TOD clock? PoOp seems to be silent.

"Do I pass your subroutine the time in seconds?"
"No, in ____s."

STCKEs? Approximate quarter nanoseconds? Tonys?


-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf 
Of Tony Harminc
Sent: Friday, February 23, 2018 11:54 AM
Subject: Re: Two summer time change questions

On 23 February 2018 at 12:03, Steve Smith <sasd...@gmail.com> wrote:
> Timer units just happen to be what the high-order word of the 
> traditional TOD clock counts.  Whether that figured as a design point 
> back in the day I have no idea.  I presume the span covered 
> (1900-2047) and the precision (specified as microseconds in bit 51, 
> implying much room for more in the last 12 bits) were more important 
> considerations.  Just my guess, though.

Just a note on terminology that we seem to need every ten years or so:

Timer Units are not TOD clock units. Timer units are approximately
26.04167 microseconds. They come from the long-gone S/360 Interval Timer, which 
was the fullword at location 80 (x'50'). This was defined so that bit position 
23 is decremented every 1/300 second, which conveniently allowed an 
implementation that decremented either bits 21 and 22 every 1/50 second, or 
bits 21 and 23 every 1/60 second, thus being able to run on a 50 or 60 Hz power 
line. Of course only the smallest 360 models actually used the power frequency 
for timing, but the definition lives on.

Timer Units are still referenced in various places in z/OS, for example the TU 
operand on the STIMER[M] macro.

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