1) the static keyword is essentially a way to maintain the space in memory for a variable. This can be used for several reasons: maintaining the value of variable between function calls as welll as maintaining internal linkage (i.e. only maintaining the variable within the file). 2) The volatile keyword essentially tells the compiler that the variable's value may be determined by things other than the program it's running (e.g. the hardware). It stops the compiler from optimizing the storage of the variable by caching for example. 3) The constant keyword essentially tells the compiler that once the variable is set to some value, it may not be changed. This can be advantageous because the compiler may then optimize storage of the value of the variable,knowing that it will no longer change.