Service Bus Premium Messaging provides resource isolation at the CPU and memory level so that each customer workload runs in isolation. This resource container is called a messaging unit. Each premium namespace is allocated at least one messaging unit. You can purchase 1, 2, 4 or 8 messaging units for each Service Bus Premium namespace. A single workload or entity can span multiple messaging units and the number of messaging units can be changed at will. The result is predictable and repeatable performance for your Service Bus-based solution.
Not only is this performance more predictable and available, but it is also faster. Service Bus Premium Messaging builds on the storage engine introduced in Azure Event Hubs. With Premium Messaging, peak performance is much faster than with the Standard tier.