JP> IM> Is this true of _all_ versions of OS/2, that they all use the
JP> IM> RTC for for their TOD clock?
JP>
JP> On a PC, what else *can* they use ?

DOS uses internal counters. It only reads the RTC when it boots. It only 
writes the RTC when you set the system time.


JP> Indeed, you'll be hard pressed to find *any* general purpose
JP> operating system on any platform (apart from very old versions of
JP> DOS) that *doesn't* use real-time clock hardware for its system
JP> clock.

Not to be contradictory, but I think that you and I probably have 
different definitions of both "general purpose" and "very old". [:)


JP> Even operating systems such as Xinu use RTC hardware of some sort.

"Of some sort" leaves your butt covered pretty good. [:) Lots of room 
for later justifications. [:)


JP> IM> Is the 2079 a C thing?
JP>
JP> No.  The limits of 32-bit implementations of the C language and the
JP> C++ language are 2038-01-19 and 2106-02-07, respectively, depending
JP> from whether the underlying type of `time_t' is signed or unsigned.

As has been explained, but thank you for the precise dates.


JP> The limits of 64-bit implementations of the C language and the C++
JP> language are somewhat higher.

Understandably. [:)


JP> The year 2079 limitation is due to the "windowing fix" employed to
JP> solve the problem that the PC's RTC chip in most PCs does not update
JP> the century byte in NVRAM when the year byte rolls over from 99 to
JP> 00.

Because of my job I would be very, very interested in hearing any 
factual information concerning an RTC used in a PC which _does_ update 
the century byte.


JP> The original RTC chip that was used didn't *have* a century
JP> byte.

Again, if you have any factual information regarding RTC's which _do_ 
directly employ a century byte, I would be interested in hearing about 
it.


JP> On most PCs the area where the century is stored is not one
JP> of the RTC registers, but is just an ordinary NVRAM area.

Yes, I have quite a bit of experience with that, thank you.


JP> The
JP> windowing fix works on the assumptions that years 80 to 99 are in
JP> the 20th century and years 00 to 79 are in the 21st century, and
JP> patches the century byte accordingly.

Very, very sad. DOS is good until 2099. The RTC/CMOS itself is good up 
to the year 9999. Too bad that IBM felt that they had to break that.


JP> Of course, this is a textbook case of a software bodge to work
JP> around a bad (or at least exceedingly shortsighted) piece of
JP> hardware design.

Yes, I agree. And I've heard that criticism of the AT's RTC before. 
Could you give me the part number for an RTC which was readily available 
in 1983 that tracked real years -- "1983" instead of just "83"?

Thanks for the reply and the additional information. Take care and TTYL.

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