As far as I know, you cannot disable the concept of virtual memory in Linux, at least not without totally rewriting it. It's an integral part of the memory management and lots of stuff simply would cease to work if you could disable it.
mmap call can be used to map a file or a device to a part of an application's virtual memory (every application has 4 GB virtual memory on 32 bit, and 16 EB on 64 bit). For example, an application could
mmap several megabytes of the hard disk into its own virtual memory. It could then access this part of the hard disk just by accessing its own memory—the kernel will automatically fetch the required data from the hard disk, store it in the RAM and return this data to the application. If you could disable virtual memory, this application would now no longer work.
On the other hand, swap can be disabled very easily, just by running
swapoff -a or not setting up swap partitions in
/etc/fstab at all.