This is an excerpt from a topic'Bypassing Windows NT's Virtual Memory System' which I found on some website:
Windows NT includes a boot option, /maxmem, which specifies the maximum amount
of memory NT is allowed to use. This boot option is specified in the c:\\boot.ini
file; for example, the following line limits Windows NT to using 128MB of RAM:
multi(0)disk(0)rdisk(0)partition(1)\\WINNT="Windows NT 4.0 " /maxmem=128
Windows NT will use the first (starting from address 0) 128MB of memory. The
memory above 128MB is available for any driver to utilize. For example, a frame
grabber driver can utilize this Non-NT memory for storing images, without
the 60% DMA space overhead imposed within Windows NT drivers ( frame grabbers
by Matrox and EPIX utilize this ). Developers can also utilize this memory via
the MEMIO example driver given in the Windows DDK. The primary advantage of
using this upper memory instead of user-memory is that it is not virtual, and
thus not swappable ( which provides more deterministic processing of large data
I've underlined the most interesting parts.
I'm interested to know if somebody has tried to measure a Memory Bandwidth of Non-NT ( Non-Virtual ) memory and has
some performance numbers?