-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Carlos E. R. wrote:
On Saturday, 2009-10-31 at 11:12 -0000, G T Smith wrote:
The CMOS clock was not part of the original PC, it was an add-on card invented later. I think they still use the same chip, or an equivalent. And read access to it was (is?) slow, so it can not be used for timing operations.
The IBM PC (1981) did not have a CMOS hardware clock, but from the PC/AT (1984) onwards it was standard. The situation with intel based non-IBM kit (it did exist in 1981) is a bit more complex (but I do remember powering up such early machines without needing to enter the date). The IBM machines were technically solid (in more ways than one :-) ), but not necessarily bleeding edge for the time.
Hmm... isnt this what ntpd does, occasionally check the upstream server and initiate a resync process if things have drifted too far. Using cron is effectively making time synchronisation process dependant on another time related process.
It does more than that. It also adjusts (slowly) the speed of the clock, for example, and never "jumps" the time, so that processes that rely on the clock are not affected during the adjustments.
Should have put either graduated or controlled before resync.. it also IIRC allows for things like network latency (which is a bit problematic to handle well with a sequence of unrelated one off time checks)...
ntp was created because of the need to keep system clocks accurately
Netdate uses ntp protocols to synchronise with a ntp server. (as does rdate)... so....
But the clock is jumped, and the speed is not altered. It is not the same method.
Me being pedantic :-) ntp the protocol is not quite the same as ntp(d) the program(s). As for clock speed alteration I do recall people telling me they used sequences of Null OP instructions to ensure accurate timing in some circumstances (!??)... Depends really what you mean by changing the clock speed, changing the hardware clock speed itself could have unfortunate consequences, changing the translation between cpu or clock ticks and calender increments is another matter. I assume the latter is meant, but I cannot find any direct reference to this in the ntp (the program) docs...
-- Cheers, Carlos E. R.
- -- ============================================================================== I have always wished that my computer would be as easy to use as my telephone. My wish has come true. I no longer know how to use my telephone. Bjarne Stroustrup ============================================================================== -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org/ iEYEARECAAYFAkrus4gACgkQasN0sSnLmgIKoACgn6zgc8fVQ31bx4tVvf2xc3dQ AuEAoKaijRw/vP1n/LIYzPCF2pFhXoRN =umVs -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org