From Urban Domeij
Lidingö, Sweden
Eugene Doherty claims that at the turn of the century a PC will invariably
reset its date to 1 January 1980 (Letters, 20 April, p 58). Though this may be
true for some systems, Doherty is seriously overstating the problem.
The date of a PC will usually not reset to 1 January 1980, unless the backup
battery is flat or removed. In some old PCs, a proprietary program retrieves
time from the machine’s real-time clock on start-up, but usually DOS does it.
While a PC will ignore any year after 2099 or before 1980, it should cope with
the next century. Whether this also applies to programs is up to the
programmer.
I’ve tried Doherty’s trick with 8088, 80286, 30886, 80486 and Pentium
machines with MS-DOS 2.1, 3.1, 3.2, 3.21, 3.30, 4.01, 5.0, 6.0, 6.2 and 6.22,
and also an 80286 with DR-DOS 6.0, all computers with different BIOSs. They all
switched to year 2000 after 31 December 1999.
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By design, the real-time clock of a PC delivers a number to the operating
system that it uses to calculate the date. Zero for this number was set at 1
January 1980. This is why no date is defined by the PC real-time clock before
1980. The date of the PC will run till 31 December 2099. Setting the date after
2079 requires all four digits to be entered. At midnight on 31 December 2099 the
date will not change, but on most systems switching off and on again will set it
back to 2000.
Still, errors due to imprecise notation of years will soar in the first days
of the new millennium. Some years ago, a 107-year-old Swedish lady got a call to
enrol in primary school. I do not shrug my shoulders at the turn of century
problem. We all have to keep an eye on computer (and human) output, to check
that it is reasonable, even if we can’t be sure it is correct.
