n Mutual Exclusion u cannot be disallowed u ex: only 1 process at a time can write to a file n Hold-and-Wait u can be disallowed by requiring that a process request all its required resources at one time u block the process until all requests can be granted simultaneously		u process may be held up for a long time waiting for all its requests u resources allocated to a process may remain unused for a long time. These resources could be used by other processes u an application would need to be aware of all the resources that will be needed