Outstanding Flexibility and Silence The be quiet! Dark Base 900 PC case is the perfect choice for all of those who expect the highest standards when it comes to modularity compatibility and design. MB-tray The motherboard tray can be repositioned vertically to suit individual space requirements or installed alongside the left panel with redefined airflow. It is removable for use as a bench table. Front I/O port Manual stepless fan controller supports up to three PWM and three 3-pin fans. 2x USB 3.0 2x USB 2.0 HD audio jacks. SilentWings® 3 The three pre-installed virtually inaudible SilentWings® 3 PWM fans with unique fan blade design rubberized fan frame and funnel-shaped air inlets provide excellent air circulation. HDD slots Flexible installation options thanks to repositionable single HDD slots. Support for up to 7 HDDs 15 SSDs and 2 optical drives. Side panel Adjustable side panel cover that you can close for absolute silence partly open for more air intake or completely open with the possibility to mount up to two optional fans. Full circuit airflow system Innovative noise-reducing vents all around the case result in an effective full circuit airflow..