** Important ** - Info on DOS 4.0                         08/19/88

Quarterdeck Office Systems
Technical Note - August 19, 1988

                    ATTENTION - READ THIS !

                 Compatibility with IBM DOS 4.0

We have tested DESQview 2.01 with IBM's PC-DOS 4.00 and found them
to be compatible. In addition, we have tested DESQview 2.01 with the
DOS 4.00 shell and found that you can use the shell to load DESQview
or alternatively you can call up the DOS 4.00 shell inside a DESQview
window.

              *** DOS 4.00 EXPANDED MEMORY BUG ***

Our tests of DOS 4.0 have revealed, however, a serious bug in the
DOS 4.00 expanded memory /X option. This bug can cause DOS 4.00 to
corrupt files or entire directories when running programs that use
expanded memory. The problem arises when using the DOS 4.00 /X option
with the BUFFERS, FASTOPEN and VDISK commands.

DOS 4.0 makes assumptions that are fundamentally inconsistent with
standard EMS 4.0 (Lotus/Intel/Microsoft expanded memory specification
version 4.0) usage. EMS 4.0 contains functions for saving and restoring
the entire memory mapping context.  Programs that need to change the
memory map use these functions to save the current map, map in whatever
memory they need, and then restore the original map.  These functions
change the entire map, including the pages of memory being used by
the DOS 4.0 /X option.  DOS 4.00, however, assumes that the map for
its pages never changes.  The result is that DOS gets confused about
which buffers are currently in memory and corrupts the file data and/or
directory data that is buffered.

As a result of our tests, we recommend that you do NOT use the /X
option when using expanded memory application programs or DESQview.


It is our understanding that IBM will be fixing the problem and making
a fix available to dealers. Until then, you risk losing files and
data when you use the /X option.

/**** SYSOP COMMENT:  We make no special recommendations as to
the version of DOS we believe is best.  DOS 4.0 seems to run well
with DESQview and otherwise.  It has a number of features, the
best of which is that it can address more than 32 meg in a single
disk partition.  The worst feature, other than the bug mentioned
above which can be avoided, is that it takes about 10K more than
DOS 3.3 ****/