The R and S series FLIP-CHIP boards were used in the original PDP-8 introduced in 1965 and peripherals. The R series was also sold as building blocks for custom hardware. They replaced the original product of Digital Equipment Corporation (DEC) which was the System Modules. The system modules were used to make the PDP-5 which was the predecessor of the PDP-8. The R series boards were replaced by the M series logic using standard TTL logic IC's when IC's became common and affordable. The M series board were first listed in the 1968 logic handbook and used in the PDP-8/I introduced in 1968. The S series boards are identical to the R series boards except faster transistors and lower value load resistors. This gave them higher speed and fanout capability. More R/S series information.
The R and S series boards have Red handles.

R Series Features:

• Useable to 2 megahertz.
• Power supply 10 and -15 volts.
• Signal level 0 volts, logic 0 and -3 volts, logic 1.
• Standard pulse 100 nanoseconds.
• Typical delay with load 60 nanoseconds.
• Typical price $20 to $30.
• Size 2.5 inches wide by 5 inches long, 18 contacts.

R series board pictures