IM>>> Is this true of _all_ versions of OS/2, that they all use the
 IM>>> RTC for for their TOD clock?

 JP>> On a PC, what else *can* they use ?

 IM> DOS uses internal counters. It only reads the RTC when it boots. 

It still uses the RTC, though.  I didn't realise that you meant "use" with the 
implicit qualification "once, at boot time".  I thought that you meant "use".  
(-:

 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.

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

I don't remember offhand (although I am confident that I have the information
somewhere), but I vaguely recall that it was MS-DOS 3.2 or thereabouts when we 
no longer had to enter the date and the time explicitly when the system was
booted because DOS read them from the RTC hardware.

I'm sure that Murray will know what version of PC-DOS was designed for the
PC/AT.  (-:

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

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

Xinu was perhaps a bad example to choose, since its original implementation,
as described in Comer's book, doesn't use a RTC since the hardware platform
doesn't have one (although it does have a heartbeat interrupt).  It has been
updated since the book was published, though, and ported to other platforms,
most notably Xinu386 for the PC.

I've replied to the non-programming part of your message, where you asked
about clock chips with proper century registers, in the OS2HW echo.

 ¯ JdeBP ®

--- FleetStreet 1.22 NR