The RCA Selectron -- The 4096-bit prototype of cylindrical design
(Circa 1945)

4096-bit Selectron
Link to 900 by 3000 pixel image (600 kb)

The 4096-bit Selectron is organized as a 4 by 1024-bit memory. Storage is on the continuous inner surface of four quadrants of a cylindrical surface, as opposed to the discrete eyelets of later designs. The glass envelope is 75 mm in diameter by 200 mm tall.

The selection electrode structure in the cylindrical design consists of stamped rings stacked vertically and rectangular bars side-by-side.

The 4096-bit device uses an odd kind of glass/metal seal for electrical pins and the vacuum tubulation. It is a variation on the design used in RCA's "Metal Tubes" where the glass beads were internal to the vacuum envelope. A complex machining, welding and stamping process made the metallic base and the individual leads (with pre-fused glass beads) were flame sealed to the numerous metal tubulations. Although inelegant and labor intensive, the electrical pin seals -- and the massive evacuation tubulation -- on this sixty year old device still hold a good vacuum. This method was replaced in later devices by the more readily mass-produced fritted disk design.