Colbalt Digital RM20-9940-C is a 20-Slot Frame Rear I/O Module (Standard Width). Rear I/O Modules may also be used for other Cobalt card models. This allows you to re-use rear modules from one card model to another. The Manufacturing Part Number (MPN) shown in the image is the common code that is used to identify multi-use rear modules. Cross-compatibility can be checked using this number.