Contents of the ATCLKFIX.DOC file
Device driver which replaces the CLOCK$ driver built into MS DOS.
Advantages are: (1) does not have the `midnight' bug (which is
present in some versions of PC and MS DOS), and (2) initializes
the DOS date from the AT CMOS battery-backed clock (which all PC
and MS DOS versions beginning with 3.0 do, but which at least one
replacement clock drivers does not).
Place the following line in the CONFIG.SYS file on your boot disk
(usually the C: hard drive):
where describes the subdirectory in which ATCLKFIX.SYS resides.
For example, my CONFIG.SYS file has the line
because ATCLKFIX.SYS is in the \UTIL subdirectory.
Only for use on a system involving AT-compatible hardware and the
MS DOS operating system which has the midnight bug.
Midnight Bug Description
The midnight bug is the failure of the DOS-indicated date to
advance by a day when midnight occurs, although the time does.
The midnight bug is known to be present in PC and MS DOS v2.00
and v2.10, and seems to be present in some later (viz, 3.XX) MS
DOS versions. It does not seem to be present in 3.XX PC DOS
The word `seems' is used intentionally in the preceding two
sentences when referring to DOS v3.XX. The occurrence of the
midnight bug may be due to incompatibilities between a
manufacturer-specific MS DOS version (e.g., Compaq- or Wyse-
specific version) and the machine on which it is hosted (e.g.,
The file CLOCKFIX.SYS, which is widely available on BBSs, fixes
the midnight bug in DOS 2.XX. Unfortunately, since CLOCKFIX.SYS
is DOS v2.XX software at heart, it does not initialize the DOS
date from the AT CMOS clock (DOS 3.00 was introduced concurrently
with the IBM PC AT). ATCLKFIX.SYS is, in essence, CLOCKFIX.SYS
with the date initialization capability added.
If you have an XT-compatible with the midnight bug, then (since
you don't have a CMOS clock) you should get CLOCKFIX.SYS even if
you are running DOS 3.XX.
By Mike Geyer. Any comments or bugs should be sent to me via
Channel 1 BBS (running PC Board) in Boston. Phone: (617)354-8873.
This software is hereby placed in the public domain.