To gain access to the interior, simply remove the thumbscrews holding the glass window and steel panel in place. As expected, the steel variant is lined with sound-dampening material. If you opt to go for the window-less version, you will also find such material on the main side panel.
The interior layout looks very traditional, but be quiet! has put quite an engineering effort into the front of the case. As it looks vastly different than the Silent Base 600, you are not simply being presented with a watered down version, but a brand new chassis interior. You have around 25 mm of space to work with behind the motherboard tray, but consider that the sound dampening will take up some of that depth.
The 3.5" drive trays are of the same type as you will find in the Dark Base 900. They are individual trays which may be detached and pulled out past the motherboard tray. You will also find two dedicated 2.5" brackets on the backside of the motherboard.
In the front, there are five possible placements for hard drives, but be quiet! only includes three trays. While this is enough for most, you will be hard pressed to find additional ones as be quiet! does not seem to be selling them separately. be quiet! has placed a 140 mm Pure Wings 2 fan into the front, which can take a total of two 120 mm or 140 mm units. You may also place a radiator of up to 360 mm in size there, but only if you remove the 5.25" drive bays. If you need these, a 280 mm variant should still find the space it needs. While I am on the subject of 5.25" drive bays: The ones within the Pure Base 600 are really basic, but get the job done. be quiet! has included thumbscrews for their easy and tool-less installation.
The PSU bay in the rear comes with a large opening in the floor to allow for cool, fresh air to be pulled in by the power supply's fan. Above it are the seven aforementioned expansion slots, with each cover held in place by a thumbscrew. You will find the second and final retail-grade fan within the Pure Base 600 - a Pure Wings 2 120 mm unit - in the very top.
Taking a quick look at the ceiling, it is clear that the offset mounting holes are really needed, especially if you want to go for a 280 mm radiator, for example. As you may also go for a 360 mm variant here, there is enough space above the top 5.25" drive bay to ensure it does not get in the way of a thin radiator of that size. Those opting for a thick radiator will have to sacrifice this expansion slot, however.
All the cables within the be quiet! Pure Base 600 are of the default variety. You should, as such, run into no issues while connecting them to a modern motherboard. The fan controller is powered by a SATA connector and comes with three 3-pin connectors.