Deadlock, file systems & I/O

Deadlock is the quietest failure in computing: nothing crashes, nothing reports an error — two processes simply wait forever, each holding what the other needs. It needs all four Coffman conditions at once: mutual exclusion, hold and wait, no preemption, and circular wait. Break any one and deadlock is impossible, which is why every prevention scheme targets exactly one condition. Worked example — resource ordering: if every process must request resources in increasing numerical order, circular wait cannot form, because a cycle would need a process to request a lower-numbered resource after a higher-numbered one, which the rule forbids. One rule, one condition broken, deadlock gone.