Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!mcvax!ukc!rde
From: rde@ukc.ac.uk (R.D.Eager)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Date does not change when PC is left on
Message-ID: <2224@eagle.ukc.ac.uk>
Date: Thu, 4-Dec-86 17:52:53 EST
Article-I.D.: eagle.2224
Posted: Thu Dec  4 17:52:53 1986
Date-Received: Fri, 5-Dec-86 05:47:05 EST
References: <289@rocky2.UUCP> <708@watmum.UUCP> <2763@gitpyr.gatech.EDU>
Reply-To: rde@ukc.ac.uk (R.D.Eager)
Organization: U of Kent at Canterbury, Canterbury, UK
Lines: 31


Just to clear up a slight error in a previous article.

The date rollover in DOS problem; is actually TWO problems.

First,  as  someone  said, the flag in the BIOS just says that a new day
has started, not how many new days. Thus a machine that is unused for  a
day will 'lose' a day.

Second,  the  IBMBIO.COM  code  (the  BIOS interface) has a bug which is
certainly present in DOS (MS and PC) version 2.xx. I am pretty  sure  it
is  fixed  in  3.xx;  I  looked for the faulty code and it was no longer
faulty. This bug is that there are *several* calls to  the  BIOS  timer,
but  not  all  are  to  get  the  date/time for DOS (those that are work
OK). The other calls are nothing to do with disk  file  date/time  (they
are  done  by the calls just mentioned) but with a two second timer used
for  disk  optimisation. In  a  nutshell,  the  disk  driver  tries   to
compensate for the lack of a door latch status bit by saying that a disk
can't  have  been changed for another if it was accessed in the last two
seconds (thus allowing directory/FAT cacheing). The bozo who wrote  this
bit  just  ignored  the rollover bit! Thus, if the first BIOS call after
midnight is to get date/time, fine. If it is  a  disk  access,  it  will
almost certainly get the date wrong....
-- 
           Bob Eager

           rde@ukc.UUCP
           rde@ukc
           ...!mcvax!ukc!rde

           Phone: +44 227 66822 ext 7589