RH10 MASSBUS controller
From Computer History Wiki
An RH10 MASSBUS controller is a secondary storage device controller for the PDP-10, primarily for the early models (KA10 and KI10) which had the PDP-10 I/O bus as a standard bus.
It works with MASSBUS disk drives and magnetic tape drives (such as the RP04, etc, series drives); up to 8 drives per RH10. It is paired with a DF10 Data Channel unit which performs DMA to main memory.