There are thirty two general purpose 32-bit registers.
Most instructions manipulate registers only.
In the filesystem abstraction, the operating system hides the details of how to interact with the disk hardware from the application program, allowing the application program to be unaware of the type of disk hardware used. Thus, the OS is free to move the actual location of the contents of a virtual memory page around in physical memory, as long as it fixes the address translation done by the MMU so that the program can still access the memory. In addition to simply moving the memory, the OS can remove memory pages from RAM by first writing it to the disk. If the program later tries to access that memory, a page fault occurs, where the program is suspended and the OS gains control of the processor. At ths point, the OS determines where the memory contents reside on disk, frees up a page of physical memory, and copies the on-disk copy back into physical memory.