What is a RLV12
The RLV12 was a Q-Bus disk controller from digital (DEC). The disk controller supported up to 4 units. Each unit could be either a RL01 or a RL02 disk drive. The RL01/02 disk drives had removable cartridges. The RL01 had a capacity of 5Mbytes and the RL02 had a capacity of 10Mbytes. the RLV12 controller was a quad-wide Q-Bus board.
The RL02 and RL01 were very common drives and almost every smaller PDP-11 system had one.
The RL02/01 used disk cartridges with a single platter, each platter had two surfaces and 512 or 256 tracks respectively. Each track had 40 sectors with 256bytes each, which results in the above mentioned capacity.
Different to the other controllers for the RL02/01 drives the RLV12 supports 22-bit addressing, for this it implemented an additional device register.
The first Q-Bus controller for RL01/02 disk drives was the RLV11. This controller consisted of two quad Q-Bus boards. The RLV11 had 18-bit addressing support and could only be used in Q-Bus systems with 256kbyte or less memory.
The RL01/02 disk drives were also supported on other controllers via system specific interfaces. E.g. there was an OMNI Bus controller for the PDP-8 and a controller, called RL11, for the UNIBUS. And you could use the RLV12 in VAX systems with a Q22-bus.
The drives were connected in a daisy chain to the controller and the last drive required a termination.
The RL01/02 is supported by most operating systems. Therefore, even so the capacity is very limited, a RL01/02 is a very versatile disk drive that allows to boot and run most operating systems on a PDP‑11.