How does an IOM3 improve the queue usage over an IOM2 in a Nokia 7750...

The IOM3 adds more memory to both forwarding complexes which increases the total number of queues available.

The IOM3 only contains a single forwarding complex which reduces the number of queues used.

The IOM3 allows multiple forwarding classes to be assigned to a single queue.

The IOM3 allows queues to be dynamically allocated between ingress and egress.

The IOM3 has a larger CPU capable of tracking active hardware queue utilization and adjusting memory allocation accordingly.