The major difference between these two types of patrol is implied by their names.  One of the types of patrol involves patrolling a given area, regardless of the amount of crime that has been happening there.  By contrast, the other type involves targeting particular areas where crime has been frequent at times when that crime has been most frequent.

Random patrol consists of sending officers to patrol a given area at random times and intervals.  It is done simply to prevent crime in that area, not because that area has been experiencing any particular problems with excessive crime.  This can involve officers in cars or those who are doing the classic activity of “walking a beat.”

Directed patrol is often used along with crime statistics.  The people who are in charge of allocating resources in the police department determine what areas of the city are most in need of patrol and at what times patrols are most needed in those areas.  Having gathered that data, they send patrols into the areas where they are most needed. 

Random patrols are conducted at random times and places and are meant to prevent crime in general.  Directed patrol is used to target particular places and times when certain types of crime are prevalent.