At the rear of the chassis is a 120mm exhaust fan, ATX power supply mount at the bottom, seven expansion slots, and at the top is room for a second ATX power supply. By default the top power supply mount is covered with an aluminum panel that offers pre-drilled holes for water-cooling. The Cooler Master ATCS 840 offers a removable motherboard tray to make the installation of components in this roomy case quite easy.
Inside this case there are six internal 3.5" drive bays and the 5.25" bays allow for tool-free installation. The HDD holders can be inserted and removed without any tools, but it does require screws to mount the hard drive in the holder. At the bottom of the case is room for an optional 120mm fan with a fan filter on the underside of the chassis. Should the bottom-mounted PSU fan be positioned towards the bottom, there is already a fan filter installed.
To reiterate, the ATCS 840 is compatible with micro ATX, ATX, and Extended ATX motherboards. With the removable motherboard tray, there is a cutout in the aluminum behind where the CPU socket generally is, which makes the installation of heatsink back-plates and other items very easy. The internal layout of this chassis is quite good and should have no problems accommodating a wealth of hardware.