Product gallery - Interior

Moving down a little we see a good 7 expansion slots and placed vertically is an extra slot for extra USB brackets. 

BTW the top 120mm fan (1200 RPM / 17dBA) is pre-installed. It can be connected directly to the peripheral PSU connector, or to the motherboard/fan controller. They can be PWM regulated meaning you can adjust the fan RPM and thus performance with either a fan controller or by the motherboard's BIOS PWM regulation. 

The CM 690 III B&W has 7 internal HDD trays. Three 3.5" and four 2.5" The number of 7 2.5-inch bays is reached by converting the HDD/SSD combo cages, while one is located under the ODD cage, one behind the mainboard tray, and one at the bottom. All the HDDs are installed in a removable and switchable tray. The tray can be secured tightly into the drive bay.

To install the drive, you pull it outwards the side of the tray and align screw holes on the drive with the installation pins on the tray. Once you have the drive in the tray, simply slide it back into the cage and lock it into place. The installation pins are rubber coated, preventing vibrations and noise. As stated you can convert these trays into 2.5" trays by pushing them inwards, quite handy and innovative.

The top HDD tray has an included adapter inside it that will allow you to install two 2.5" or 1.8" drives to it and can then be placed into the hard drive cage, something which is very handy for an SSD drive.