Operation of PDP-1 Sequence Break System and High Speed In-Out Channel for Effecting System Intercommunication

This document describes two methods for managing input/output (I/O) intercommunication on the PDP-1 computer.

Sequence Break System

This optional feature enables concurrent operation of multiple I/O devices by allowing automatic program interruption. It utilizes a priority chain with 16 channels, where faster devices can interrupt slower sequences to optimize computer performance. The system stores the current machine state (AC, IO, and PC) when a channel assumes priority and jumps to a dedicated routine.

High Speed In-Out Channel

Designed for high-speed devices like magnetic tape, this feature allows direct block transfers between memory and the device, bypassing the In-Out Register to minimize overhead. It reduces transfer times to a single machine cycle and operates in the background, significantly improving overall system computation efficiency compared to programmed I/O or standard sequence breaks.