🚀 go-pugleaf

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
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