Page 3 - Physical Look - Inside
Consistent with its exterior, the interior of the Fractal Design Define One Dark TG is also nicely finished with all surfaces painted matte black. To further accentuate its all-black color scheme, the back expansion slot covers and removable drive trays are painted black as well. The conventional layout has the power supply mounted at the bottom inside a shroud with the main area allocated for the motherboard. Generally speaking, everything is quite traditional as far as ATX computer cases are concerned. Let us take a closer look at what is going on inside.
The Define One is able to accommodate mITX, mATX, ATX, and E-ATX motherboards. For motherboards with back connectors, it can take up to ATX-sized boards, which you can see the location of the corresponding cutouts. The riser mounting holes are labeled for extra convenience regardless of PC building experience. No pre-installed rear exhaust fan is situated around the CPU socket area of a standard ATX motherboard, but the opening can accommodate one 120mm unit. The upper ventilation area is open with a mesh. I would much rather have, at the very least, a dust filter here, because the holes in the mesh are rather large and will not keep much out. Three 120mm or two 140mm fans or a radiator of equivalent size can be installed at the top of the case.
As shown in our photo above, we can also spot a large rectangular opening on the motherboard tray for easy aftermarket heatsink backplate installation without removing the motherboard itself from the chassis. The opening is actually large enough to accommodate pretty much anything. I mean, with something this big, unless you have some strange motherboard, it is hard not to get it right. The tallest heatsink you can install is 171mm. The perimeter of the opening is not lined with rubber, but the edges are well rounded off, so you do not need to worry about your cables being stripped accidentally.
The chassis platform is raised about 1.5cm off the ground to accommodate PSUs with fans at the bottom, because the Fractal Design Define One features a bottom-mounted power supply bay. Should you flip your PSU to have the fan at the top, a ventilation grille is present to keep the air flowing. Inside the Define One, metal bumps with rubber toppings at the top elevate the power supply up a further half centimeter just to ensure enough air is made available to your PSU. A metal bracket is designed to be attached to your power supply, and is held on by two captive thumbscrews. The ventilation grille has an externally removable dust filter pre-installed, so you will not need to worry about nasty stuff clogging your fans down the road.
There are two thermal zones inside the Fractal Design Define One, even though the shroud separating the main chamber and the power supply chamber is ventilated at the power supply. An air guide routes the intake air generated by the bottom 140mm fan into the main chamber rather than the bottom chamber. Small cables can be routed through the opening on the shroud adjacent to your power supply. If the cables do not fit through the standard openings, you can always use the other openings on the motherboard tray. Rubber grommets are present on the large motherboard tray opening to keep everything looking neat and tidy, but no other is present for cost savings. For unused cables, it can stay underneath the shroud.
Three 4-pin PWM Fractal Design Momentum 14 140mm fans draw cool air into the system from the front. They are fluid dynamic bearing fans rated at 1800 RPM, 31.9 dB(A), 79.79 CFM, and 2.26 mmH2O. Out of the box, they are daisy chained together, so you only need to connect one PWM connector to your motherboard. The fans can be swapped for a radiator of equivalent size. A layer of sound absorbing material is installed behind the front panel, used to dampen the sound emitted from these fans.
The longest video card you can fit in the Define One is 368mm with front fans installed. No graphics card is that long at the time of writing this review, but with the way things are going, we are getting dangerously close. A built-in GPU support arm is present, which slides along an integrated rail and swings out to keep those long graphics cards from sagging. It has a software rubber tip at the end, so there will never be any metal contact.
Here is a look at other side of the Fractal Design Define One Dark TG. The back of the motherboard tray is quite fundamental to good cabling. This is especially held true with the Fractal Design Define One, since it is normal practice to cables through this section. With the latest iteration, the company kept gap wide with room here for 2.5" and/or 3.5" drive installations. The amount of room between the side panel and motherboard tray is 37mm. Users will generally not experience problems if you own a power supply with thick cables.
The back panel area can accommodate a surprising number of drives. The set of brackets underneath the CPU heatsink opening in the above photo can accommodate one 3.5" or two 2.5" drives each. These brackets can be relocated to the cable routing area on the left side of the motherboard tray. Two additional 2.5" drives can be installed on the floor of the lower chamber. This is probably more than enough for most users in 2026, considering I have been using only NVMe SSDs for years now.
There is an integrated main cabling guide towards the front, where two Velcro straps and pair of removable T-shaped cable guides allow for easy organization in this area. Three additional Velcro straps are placed towards the back. Other than that, lots of openings can be found so you can fish your cables through, and they are reasonably sized to carry everything you need. There is only one rubber grommet on the main opening, and the rest are left open, which is a cost-saving measure. The rubber grommet is clipped on well, but if you rip your cables through these holes during your build, it may become loose, although it is not a significant problem.
No bottom intake fans or radiators can be installed into the Define One. The Define One can officially take power supplies up to 180mm long with an SSD installed in the location closest to the PSU. If that location is unoccupied, you can have a PSU that spans 225mm according to my measurements. If you go further and remove the air guide, you can have a PSU that basically spans the entire length of the case. Of course, this is just a trivial fact, because I do not believe something of such a size exists in the world, haha.
The Define One's I/O connector cable is a simple cable terminated by a block that connects to the power switch and front power indicator LED. Lastly, we can see a fabric-coated sound insulation material is placed over the right side panel for improved acoustic properties, just like the front panel. They are thin and occupy little physical space. They are generally flat, so it will not affect airflow inside the case either.
Page Index
1. Introduction, Packaging, Specifications
2. Physical Look - Outside
3. Physical Look - Inside
4. Installation and Conclusion
