memory and /dev/mem

Hi everyone,

I have a question about /dev/mem. It looks like /dev/mem is actually shorter that the actual physical memory available on the system, by about 600 kilobytes (seems to depend on the total size). Is there a reason for that? It happens that on some systems, the DMI table is located near the end of the memory, so we are not able to access it. Is this memory area special?

Thanks.

Jean Delvare
http://www.ensicaen.ismra.fr/~delvare/