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