In some cases, yes you do loose some ram for internal stuff, check vga bios settings memory allocation size The bigger the better for any intensive video display like a scope
... or add an internal video card who will liberate some ram too, but this is a scope loll you have interface modules / boards ....
You always loose some ram ... even on more modern stuff, for a 4gb ram, you run about 3.5 gig etc ... +/- 500 Kb are lost ...
The board will report the ram quantity, but once booted it's another thing
You could try 2x2gb some Intel D865GLC can go up to 4gb of ram ... i have one in a TDS7254 B