Complicating this simple-looking series of steps is the fact that the memory hierarchy , which includes caching , main memory and non-volatile storage like hard disks ( where the program instructions and data reside ) , has always been slower than the processor itself .
Complicating this simple-looking series of steps is the fact that the memory hierarchy , which includes caching , main memory and non-volatile storage like hard disks , ( where the program instructions and data reside ) has always been slower than the processor itself .