The clock-comparator sign control bit is part of the of the multiple-epoch
facility, which has been on all machines starting with z14.
It is up to the operating system to decide when it should turn on the
clock-comparator sign control bit.
z/OS 3.2 does that only if directed by an undocumented control, so the typical
customer does not have the option.
I would anticipate that some future release will automatically make the
decision based on the value of the TOD when the system is IPLed.
The customer should not need to be involved in that. z/OS 3.2 will be out of
support long before a production system could experience the TOD wrap.
Jim Mulder
-----Original Message-----
From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> On Behalf
Of Paul Gilmartin
Sent: Saturday, April 12, 2025 5:19 PM
To: ASSEMBLER-LIST@LISTSERV.UGA.EDU
Subject: Re: Store-Clock-Fast Facility
On 4/12/25 14:10, James Mulder wrote:
> Current field releases of z/OS do not turn on the clock-comparator sign
> control bit.
> z/OS 3.2 will be the first release that can turn it on (but only on test
> systems).
> ...
You can raise more questions than I ask.
o Is the clock-comparator sign control bit independent of the multiple-epoch
facility?
o "only on test systems" does the customer have the option to configure a
particular system as "test" or "production"?
> -----Original Message-----
> From: Jonathan Scott
> Sent: Saturday, April 12, 2025 1:13 PM
>
> "When the multiple-epoch facility is installed in the configuration and the
> clock-comparator sign control is one, comparison follows the rules of signed
> binary arithmetic."
>
--
gil
