Host Bus In-Order Queue Depth

Common Options : 1, 4, 8, 12

Quick Review

This BIOS feature controls the use of the processor bus' command queue. Normally, there are only two options available. Depending on the motherboard chipset, the options could be (1 and 4), (1 and 8) or (1 and 12).

The first queue depth option is always 1, which prevents the processor bus pipeline from queuing any outstanding commands. If selected, each command will only be issued after the processor has finished with the previous one. Therefore, every command will incur the maximum amount of latency. This varies from 4 clock cycles for a 4-stage pipeline to 12 clock cycles for pipelines with 12 stages.

In most cases, it is highly recommended that you enable command queuing by selecting the option of 4 / 8 / 12 or in some cases, Enabled. This allows the processor bus pipeline to mask its latency by queuing outstanding commands. You can expect a significant boost in performance with this feature enabled.

Interestingly, this feature can also be used as an aid in overclocking the processor. Although the queuing of commands brings with it a big boost in performance, it may also make the processor unstable at overclocked speeds. To overclock beyond what's normally possible, you can try disabling command queuing.

But please note that the performance deficit associated with deeper pipelines (8 or 12 stages) may not be worth the increase in processor overclockability. This is because the deep processor bus pipelines have very long latencies. If they are not masked by command queuing, the processor may be stalled so badly that you may end up with poorer performance even if you are able to further overclock the processor. So, it is recommended that you enable command queuing for deep pipelines, even if it means reduced overclockability.