IBM/XT Y2K Compliancy

From: Chuck McManis <>
Date: Sat Aug 7 17:04:19 1999

And just to put some "definition" around "Y2K Compatible", from these
comments below and others they prove without question that the original
machines from IBM called the PC/XT and the PC/AT are *NOT* Year 2000
Compliant. They do not behave properly with respect to their dates *AS A
SYSTEM* when the internal notion of date goes from 1999 to 2000.

This has *NOTHING* to do with the question of whether they are *USABLE*
after the year 2000, which as others have pointed out is simply a matter of
either software patches, manual intervention, or "agreeing" to run their
notion of the date/time differently than the actual date and time.

This distinction may seem petty but it is important. Many things may happen
at the beginning of the year that will require _manual_ intervention
because the _system_ was not compatible. By certifying something as "Year
2000 Compliant" a manufacturer certifies that the behavior of the system
will be no different during the roll over from 1999 to 2000 than it was in
any other year.

Hopefully we can put this stuff to rest, but I doubt it.

Some one else wrote:

>> I have five 486 boards that hae older RTC that roll over from 1999 to 1980!
>> they do however set manually to 2000!

Tony Duell wrote this stuff:

>Most PC real time clock chips keep the year in 2 parts. A counter, 0-99
>(BCD) which is automatically incremented when the month goes from
>december to january, and a byte in the CMOS RAM (normally set to 19 or
>20) which holds the century. The latter is _not_ automatically updated.

>Now, some PC BIOSes/OSes will take an invalid (too early) year as being
>1980. So the clock rolls over from 1999 to 1900, and the _software_
>changes that to 1980 (as otherwise it's too early a date). That's why you
>can manually set them to 2000.

>The chip itself is working correctly (as designed). The software is
>misusing it ;-).
Received on Sat Aug 07 1999 - 17:04:19 BST

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