# In case of program overlays; is it necessary to have error handling routine in memory, regardless of error?

I came accross the question regarding program overlays,

Program1 is of 100kB and program2 is of 90kB and common code is 10kB and overlay driver is 20kB and error handling routine is 50kB, min memory required when there is no error?

according to me it should be 100 + 20 + 10 = 130; as there is no error..
but ans is 180; they are considering error handling routine also in account..

I am not getting why error handling routine, if there is no error?