The ASUS P8Z77-V Premium Thunderbolt Implementation
The first of two motherboards we have seen with a Thunderbolt implementation is the ASUS P8Z77-V Premium. Besides having other killer features like support for 4-Way SLI and CrossFire, a new SSD caching technology, and on-board 32GB mSATA SSD for caching, ASUS has integrated the Cactus Ridge Thunderbolt controller for a single port of TB.
This Z77 motherboard from ASUS might look like most of its other models, but the P8Z77-V Premium was the first Thunderbolt motherboard to get certification. In the documentation that ASUS provided with the motherboard there were some very interesting implementation notes in which ASUS makes the claim that its Thunderbolt motherboard will best the competitions.
The first notable change comes in the trace length for Thunderbolt compared to USB 3.0 – where the USB controller is separated by as much as 10 inches of traces, the Thunderbolt port is at most 2 inches from the controller. The goal here, as with all of the notes below, is to provide the most stable, compatible and best performing solution possible.
The closeness of the traces will result in several other differences as well. First, the trace layout uses much more signal routing space in order to prevent crosstalk – and electrical noise – that would hinder performance. The traces are routed in an arc shape as well, as opposed to being at 45 degree angles as you see with the USB 3.0 connections. This can reduce the impedance of the connection and improve connection reliability. Also worth noting is that the Thunderbolt connection cannot be moved between layers of the PCB whereas the USB 3.0 traces can move between 2 layers and remain stable.
According to these advances, ASUS claims that its implementation for Thunderbolt provides 3.8% better signal rise time, 3.1% better signal fall time and 7% overall impedance improvements.
ASUS dives even deeper into the physical changes they are using by using a hollow layer below the connection, caps and inductor pads along the Thunderbolt traces. The return path has also been modified to be shorter than standard to dissipate the signals more quickly to ground and reduce electromagnetic interference. If all of this goes past your knowledge of electrical engineering, just know that ASUS has done seemingly everything possible in order to make sure that the signal paths on the P8Z77-V Premium are as as perfect as possible.
I mentioned earlier that the daisy chaining of devices created some issues for hardware and software developers. This is in relation to the ability to "hot plug" a device; installing it without having to reboot or shutdown your machine. While the Thunderbolt connection can support six levels of daisy chaining, the Windows operating system can only handle one level of PCIe device hot plug, thus causing issues with installing and removing devices from a running system. The first implementations of Thunderbolt we saw prior to this release required to you reboot your machine after connecting a device, even if it was the first (and only) device in the chain.
ASUS has modified the BIOS/UEFI to help Windows handle these hot plug events with Thunderbolt and can correctly allocate the required resources to allow for dynamically installing hardware. And while ASUS has done much to help the situation, we learned from both Intel and Promise / Pegasus that a driver fix would indeed make all the difference in our experience. While drivers aren't technically required for Thunderbolt to just "work" in its PCI Express switch modes, in order for each device on the Thunderbolt connection to function completely you will likely need to install drivers.
The ASUS P8Z77-V Premium motherboard sports a single Thunderbolt connection with bi-directional 10 Gbps bandwidth available to it. Future controllers will allow for more than a single Thunderbolt connection on a motherboard but I am curious to see how that will integrate with DisplayPort and actual monitor support.
The Cactus Ridge controller itself is seen here directly behind the Thunderbolt connection, a result of requirements and the engineering work of ASUS.