has to hold the operating system and all of the
device drivers that it uses. If you are working with a network than the network
device driver alone could add up to around 100KBytes.
The first and
most effective way of clearing more of the conventional memory area is make use
of the HMA. Many device drivers can load themselves into the HMA. If you are
using MS-DOS 5 then it can load a full 64KBytes of itself into the HMA. Of
course the problem is that it is a single 64KByte area and once it is used up
that is it. In most cases you should reserve it for the software that can make
the most use of it, i.e.load the largest into the HMA. The HIMEM.SYS driver can be set to deny
access to any software that doesn’t request sufficient of the HMA to make it
worthwhile.
After the HMA
has been used the only other possibility is to make use of free areas of the
memory map above the 640KByte limit. If you recall, this 384KByte area, the
Upper Memory Area or UMA, isn’t any different from the first 640KBytes of
memory, it’s just that it is used for a different purpose. If there is an area
of the UMA that isn’t being used for a ROM, video
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