In nearest cylinder next, we cant fix the direction in which go next
but in Elevator , first we fix the diection then go only that direction and then come back to opposite direction
like if we have 10,50 request and head is on 20
then nearest cylinder next , 20->10->50 total seek time 10+40=50
elevator 20->50->10 total seek time=30+40=70 ( direction is fix toward 50)