Mini-ITX motherboards can be found in almost every motherboard manufacturer's portfolio these days. Asus has several of these small-form-factor boards in its lineup, capped off by its enthusiast-oriented Republic of Gamers (ROG) line. The Impact models are Asus' Mini-ITX boards for the Republic of Gamers, and the company has updated the concept for for the Z170 platform with its Maximus VIII Impact.
The limited board area of the Mini-ITX standard places tight constraints on what features and functionality can be integrated into these boards, especially for expansion slots. Enthusiast mobos like the Impact only come with one PCI Express expansion slot, and that space will almost certainly be occupied by a graphics card. As a result, it's important that the board satisfy as many end-user requirements as possible out of the box.
The Maximus VIII Impact keeps with the same basic layout as its predecessors: the Z97 Maximus VII Impact and the Z87 Maximus VI Impact. This is certainly not a bad thing, because the formula obviously works. The biggest difference in aesthetics is that the expansion ports on the Maximus VIII Impact are now clad in muted grays rather than the striking red of previous designs.
Dimensions of only 6.7" x 6.7" (17 x 17 cm) leave Mini-ITX boards with less than 40% of the PCB area compared to their full-sized ATX brethren, and half as much as their microATX counterparts. That's not a lot of room to for onboard components, especially when we're still dealing with the same LGA 1151 CPU socket and 288-pin DDR4 DIMM slots from those larger motherboards.
To make the most of Mini-ITX's limited real estate, Asus builds upwards. The best example of this strategy is the daughterboard seen running along the top edge of the board. This houses the Impact's VRM components.
The Maximus VIII Impact's daughterboard holds a premium eight-plus-two voltage regulation complex. Digital PWM controllers power eight phases for the CPU and two for the memory. This design should let the Impact hold its own against much larger motherboards in the VRM department. A slim ROG-branded heatsink cools these components. The few VRM components found around the CPU socket feed the processor's system agent and I/O voltage rails. Just as a reminder, Skylake processors once again rely on the motherboard's VRM to supply each of the processor's input voltage rails—the fully-integrated voltage regulator (FIVR) used by previous-generation Haswell chips has fallen out of favor.
Voltage regulation isn't the only area where we see Asus reaching for the skies. Onboard audio and Wi-Fi also have their own separate riser boards. Those vertical elements are large enough to interfere with CPU coolers that branch out from the socket. This complicates clearances around the CPU socket, which is already closer to the DIMM slots than we'd like.
Here are some measurements showing the distances between the CPU socket and nearby components:
On larger boards, we're usually most concerned with the proximity of the first PCIe x16 slot to the CPU socket. In the case of the Maximus VIII Impact, it's the audio riser that's potentially most troublesome. Thankfully, that riser is only 36 mm tall. The VRM daughterboard is slightly taller, at 42 mm. Those who plan to install big heatsinks that overhang the CPU socket area should check clearances to avoid any nasty surprises.
Tight clearances on the Impact aren't just a problem for large air coolers. The beefy water block of the Cooler Master Nepton 240M liquid cooler we use for testing runs afoul of the capacitors to the left of the CPU socket. This conflict prevents the block from making sufficient contact with the CPU's heat spreader, removing two of the four possible orientations as workable options. Clearance issues between the DIMM slots and the hose connections to the block ruled out a third possible orientation. We finally pointed the hose side of the water block toward the I/O ports.
The two DDR4 DIMM slots can hold up to 32GB of memory when they're filled with 16GB sticks. For single-DIMM configurations, Asus recommends using the slot closest to the CPU socket. To get the best performance, though, you'll need to fill both slots for dual-channel operation. With the DIMM slots caught between the VRM daughterboard and the PCIe x16 slot, swapping DIMMs is likely going to involve removing the video card first. That said, I'm happy to see two full-sized DIMM slots rather than the SO-DIMM alternative. Asus also uses slots with locking mechanisms on only one end, which makes life a little easier.
The Maximus VIII Impact's single x16 PCIe slot is fed with sixteen Gen3 lanes coming from the processor. Once the graphics card is installed here, getting to the SATA ports may prove difficult. That problem will only get worse once the board is in your case, so be sure to connect your storage before installing your GPU.
Thanks to Intel's 22-nm fabrication process, the Z170 chipset has a TDP of only 6W. This allows Asus to get by with the slim heatsink seen directly above the PCIe x16 slot. Immediately to the left of the chipset heatsink we can see Intel's Alpine Ridge USB 3.1 controller, labeled Intel DSL6540. For the Maximus VIII Impact, Alpine Ridge is acting purely as a USB 3.1 controller with no support for Thunderbolt 3. It is connected to four of the chipset's Gen3 PCIe lanes, endowing it with 32 Gbps of bandwidth. The tiny Intel chip to the left of the PCIe x16 slot is the I219-V Gigabit Ethernet controller. It connects to a single PCIe lane from the chipset.
Here's a graphical representation of how the Maximus VIII Impact uses the platform's PCIe lanes:
Now, on to the Impact's storage subsystem.