The Console of PDP-3 has controls and indicators for the use of the
operator. Fig. 4 is a close-up of the control panel of PDP-1, the 18 bit
version of PDP-3. All computer flip-flops have indicator lights on the
Console. These indicators are primarily for use when the machine has
stopped or when the machine is being operated one step at a time. While
the machine is running, the brightness of an indicator bears some
relationship to the relative duty factor of that particular flip-flop.
Three registers of toggle switches are available on the Console. These
are the Test Address (15 bits), the Test Word (36 bits), and the Sense
Switches (6 bits). The first two are used in conjunction with the
operating push buttons. The Sense Switches are present for manual
intervention. The use of these switches is determined by the program
(see System Block Diagram and Skip Group Instructions).