The Process (进程) is blocked while the necessary instruction is being located and read in from Main Memory to CPU
Usually happens when not all Process has its whole program codes in the Main Memory
3 Possible Causes
Lazy Allocation
Not allocating Main Memory until it is actually needed
By delaying the actual allocation, we speed up startup time & eliminate allocation entirely if it isn’t used
But this means slower execution speed because Main Memory is only allocated when needed & we are risky to run-time allocation errors aka more likely to crash when running the app halfway
Swap
The required data or instruction are in the Swap Space
