They are perforated, to resemble the punched paper tape Tutte was so familiar with, and when viewed from one particular direction reveal an image of Tutte's head and shoulders.

BBC: Suffolk

Before the introduction of magnetic tape, digital storage for early computers used punched cards, paper tape as well as more exotic technologies such as mercury delay lines and the phosphors on cathode ray tubes.

FORBES: Magnetic Tape Turns 60

It would use magnetic-tape storage to replace punched data cards and printers to list the content of the tape.

CNN: Genesis of the computer