RAM-DISK is a peripheral that presents a generous amount of Random Access Memory as it it were a mechanical disk. It is intended to overcome the limitation of 4KWords of main memory imposed by the HER/12 architecture.
RAM-DISK devices can be used for temporary storage. For example, they can be employed to implement sorting algorithms such as Merge Sort, swap devices, support for Overlaid software, and others.
Being a peripheral, a RAM-DISK device connects to the CPU via I/O channel and it is treated by the CPU as a block device. Being much faster than a real disk, transfer from/to RAM-DISK is not synchronized via interrupts but (if necessary) via WAIT signal.
A "side channel" is a path way between devices so they can talk to each other without CPU intervention. It can be useful, for example, for DMA file transfers taking place concurrently with programs running at the CPU.
This specification is an effort to standardize the implementation details of the Side Channel for the sake of compatibility.