mmap & /dev/shm

We have a in-house application that uses mmap to pull a file into memory. I can't seem to find any info on where this file is stored in memory. I know that it is shared memory. But does the /dev/shm have anything to do with it. Isn't shm just a tmpfs? Also can shm be disabled? I have a machine with 16GB and 8GB then goes to the shm. Does this only allow mmap to use the other 8GB or is all 16GB accessible to it? These are the questions I have been trying to figure out for over a week now. Not many answers on google and no one has seemed to ask this before. Also is mmap the fastest way to get a file from disk to memory? Any help appreciated. Thank you, Brad Dameron SeaTab Software www.seatab.com