Earlier this month, MSI opened fire on Gigabyte over the company’s support of PCI Express 3.0. MSI made its claim through a slide deck press release, where it boasted that its motherboards featured true PCIe 3.0 support and that Gigabyte’s boards did not.

Tom’s Hardware contacted Gigabyte for its side of the story and now, having talked to both companies in depth about the issue, and now seemed to have found the truth to the stories from both side, somewhat.

Gigabyte says it can achieve some PCIe Gen 3 functionality via three different approaches:

One PCIe 3.0 Card, No Switches Required

Gigabyte’s existing LGA 1155-based motherboards should, with a simple BIOS update, support upcoming Ivy Bridge processors. Drop in a processor, and, without any special switches, capacitors, or resistors, enable a single 16-lane PCI Express 3.0 link. That’s connectivity for exactly one PCIe 3.0-capable graphics card.

Now here’s the thing: although the slide below suggests that Gigabyte is the only vendor able to do this, it isn’t. Any vendor claiming Ivy Bridge compatibility on a P67 or Z68 motherboard is expected to enable one 16-lane slot in the exact same manner. Again, because there aren’t any special surface-mount components needed, the higher data rate just works.

Two PCIe 3.0 Cards with Gen 2 Switches

The second situation is the catalyst for MSI’s presentation. When you drop in two PCIe 3.0-capable graphics cards into certain Gigabyte P67- and Z68-based boards with an Ivy Bridge processor, 16 lanes of connectivity get split between two x16 slots. If the motherboard only has PCIe 2.0 switches, Gigabyte says the first slot will operate at PCIe 3.0 data rates, but drop to eight lanes. The second slot will only operate at PCIe 2.0 data rates (again, using eight lanes). Effectively, that halves bandwidth shifting from eight to 16 lanes and halves it again switching from third- to second-gen data rates. Of course, we don’t have the cards to verify those claims. However, we will be double-checking once add-in boards become available.

Now, it remains questionable whether forthcoming graphics cards natively employing PCIe 3.0 will actually see a benefit from the third-gen technology. But it’s a matter of principle; I get it. You buy a CPU with PCIe 3.0 and you want your motherboard to support it.

Two PCIe 3.0 Cards with Gen 3 Switches

Gigabyte does sell a (one) motherboard with newer third-gen switches on it: the Z68-based G1.Sniper 2. That platform is expected to split up 16 lanes and yield two x8 slots operating at 8 GT/s. Everything else, the company claims, will operate in a mixed second- and third-gen environment.

In comparison, MSI’s boards with third-gen switches should all split Ivy Bridge’s PCI Express into one x16 or two x8 PCIe 3.0 slots.

Gigabyte adds, however, that all future Z68-based models will incorporate third-gen switches. Moreover, revised versions of existing platforms with those same third-gen systems should start surfacing in October, according to company representatives.

The NF200 Exceptions

Interestingly, with all of this back and forth about PCI Express 2.0 and 3.0, there’s another implementation that deserves mention: motherboards with Nvidia’s NF200 on-board.

In taking 16 lanes of second-gen PCIe from Sandy Bridge CPUs (and, in the future, Ivy Bridge CPUs), NF200 multiplexes that traffic into a pair of 16-lane PCIe 2.0 links. Two PCIe 2.0 16-lane links should deliver the same throughput as two PCIe 3.0 eight-lane links. You’ll still run into a theoretical bottleneck on the CPU side, since NF200 is a second-gen switch.

Only the future can tell us whether the next generation of PCI Express 3.0-capable graphics cards will need third-gen slots. However, given the fact that eight- and 16-lane second-gen slots are still pretty much interchangeable four years after PCIe 2.0 was first productized, we’re not anticipating notable benefits right off the bat.

SOURCE via Tom’s Hardware