Come inside, come inside
Given what we've seen of the Define Nano S so far, it shouldn't come as a shock that the interior of this case is a lot like the Define S's, just smaller.
The "pegboard" area in front of the motherboard tray is meant to offer builders a mounting spot for liquid-cooling hardware like pumps and reservoirs. The pegboard also eliminates airflow obstructions if those components aren't being used.
A new "cheese plate" in front of the power supply mount is pre-drilled for a variety of common liquid-cooling pumps. This plate can slide forward and backward on its adjustable mount, and it also doubles as an extra 3.5" drive mount if the single 3.5" sled behind the pegboard area isn't enough room for mechanical storage. If the plate isn't needed, builders can remove it and install a 120-mm fan or radiator in its place.
Like many other Mini-ITX cases, the Nano S is designed for a full-size ATX power supply. That choice could be a problem, since it means only a precious few millimeters stand between the top of the power supply and the graphics card cooler if one is installed. Fractal cautions builders to only use cards whose coolers fit within a dual-slot form factor with this case.
Even with a standard-length ATX power supply, the expansion card slots are so close to the top of the PSU that ventilation could be a problem for shorter coolers. Adapting an SFX PSU to the Nano S might give graphics cards more breathing room, but the cables included with those PSUs are often much shorter than those of their ATX brethren. We'll have to see how this potential pain point plays out in our tests.
At the top of the case, Fractal includes its usual complement of fan and radiator mounting points under the ModuVent panel. A 240-mm radiator can fit up here, but 280-mm heat exchangers can't. Fractal cautions that DIMMs taller than 35 mm might cause clearance issues with 240-mm radiators, too. Check the handy, clearly written manual for full clearance information. Those sticking to air cooling can add two 120-mm or 140-mm spinners here, too.
On the back side of the motherboard tray, we get another 3.5" drive mount and a dual-SSD drive sled. Both of these sleds are held in with thumbscrews, but builders will still have to pull out their screwdrivers to actually affix drives to them. Fractal also includes three hook-and-loop straps in strategic positions to make cable routing easier. Room for cables behind the motherboard tray is precious in this case, though: half an inch at its narrowest point, expanding to an inch and a half behind the 3.5" drive mounting area. While Mini-ITX systems aren't often full of cables, this area feels pretty tight in the Nano S, regardless.
As Mini-ITX systems go, building in the Nano S is an entirely straightforward process. I only have some minor issues with the case's interior layout.
Our MSI A88XI AC motherboard is laid out with most of its ports and power connectors toward the top of the case, so the Nano S's top two cable-routing grommets get crowded. The 24-pin and eight-pin ATX power cables, the two SATA cables, and the front-panel connectors all have to pass through these grommets, and they have to be angled back tightly to reach their associated ports and pins.
Most new Mini-ITX mobos seem to be laid out with the 24-pin power connector at the right edge of the motherboard these days, so I doubt this issue will rear its head with a more current system. The main grommet near the power supply gets pretty crowded, too, but neither set of grommets felt underprovisioned for the average Mini-ITX PC.
Those minor complaints aside, if you can build an ATX system in a mid-tower case, I'd argue you can build a Mini-ITX PC inside the Define Nano S. Given the careful assembly-order requirements and clearance headaches I've had with other Mini-ITX cases, the refreshing simplicity of the Nano S is a relief.