Q59890: Minimum Extended Memory (384K) Causes CV 3.00 to Use Extra RAM

Article: Q59890
Product(s): See article
Version(s): 3.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr HIMEM | mspl13_basic
Last Modified: 27-SEP-1990

Real-mode CodeView (CV) Version 3.00 is documented as being able to
run in extended memory as long as there is at least 384K of extended
memory available. This 384K minimum is accurate as far as CV being
able to utilize the extended memory, but it is not enough for CodeView
to remove all of itself from conventional RAM. In fact, a system
configuration with only 384K extended memory will result in LESS
memory being available for the debuggee (the program being debugged)
than if no extended memory is utilized at all.

The CodeView 3.00 documentation states that "if HIMEM.SYS or another
extended-memory driver is installed, all but 16K of CodeView, plus all
of the symbolic information for the program you are debugging, are
placed in extended memory." But, for CodeView to truly work with this
16K "footprint" in conventional memory, a minimum of approximately
600K extended memory must be available.

When no extended memory is available, CodeView normally utilizes
overlays to keep as much of itself out of memory as possible, so that
the debuggee can have more space to load. (The new /Dnnn option
actually allows you to specify the size of the overlays -- a bigger
overlays means CV runs faster, but a smaller overlays mean a bigger
program can be loaded for debugging.)

Once CodeView detects extended memory, it assumes that overlays are no
longer needed, since CV itself and the debuggee's symbolic information
will both (supposedly) be loaded into extended memory. However, the
result may be that CodeView seems to get bigger because what Codeview
can't fit into extended memory is loaded into conventional memory.

Since no overlays are used, this can result in a much larger
footprint. For instance, if the minimum of 384K extended memory is all
that is available, then the footprint will be well over 200K.
Obviously, as the amount of extended memory is increased from 384K,
the footprint will shrink accordingly.

The /X command-line option instructs CodeView to use extended memory.
However, CV will automatically detect extended memory and use it if it
is available. Consequently, if the /X option is not specified, CodeView
will still use extended memory.

Thus, if you have a limited amount of extended memory and decide to
run CodeView in conventional RAM only, you have two options. You can
explicitly specify /D (for example, /D16) to tell CodeView to use
overlays, or you can remove (or comment out) the line in your
CONFIG.SYS file that loads the extended memory driver (HIMEM.SYS) and
reboot.

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