🚀 go-pugleaf

I use Turbo Pascal and work on an AT with 1 M memory.
The question that I have is: 

How can I make use of the memory between 640K and 1M ? 

Turbo Pascal provides functions to load overlay-files
into this area once an EMS driver is installed. Where do I get an
EMS driver from? Are EMS drivers compatible with all AT's (i.e.
will a specific EMS driver work on all compatibles)? 

In addition to that: Is it possible to use memory in the area
of 640K to 1M as a heap? I'm pretty certain that this is impossible
but maybe I am wrong.

Since EMS is controlled by MS-DOS is there a way of allowing *only* the
overlay file to make use of it, but keeping other applications (running
concurrently; e.g. networking software) from using it?

If you can answer any of my questions I would appreciate your help.
If you know of a book or magazine that gives me good, detailed, and
understandable information on this subject, I would be thankful as
well.

Thnx again.