How did Colossus store data electronically?

The Colossus computer did not store data in the way modern computers use memory to hold programs or large datasets. Instead, it was a special-purpose machine designed to perform specific cryptographic calculations at high speeds using electronics.12

Colossus processed data by reading a single paper tape containing the encrypted German message. Crucially, the "key" data—which was required to decrypt the message—was not stored in a traditional memory device but was generated electronically by the computer’s own circuits. By generating this key data internally, the machine eliminated the need for a second input tape, which had caused synchronization issues in earlier, less reliable machines like the "Heath Robinson".1

While Colossus pioneered the use of vacuum tubes for high-speed computation and embodied the insight of storing data electronically within the machine, it lacked the stored-program architecture that would later define general-purpose computers. Unlike later machines that used components like mercury delay lines to store bits, Colossus relied on its electronic circuitry to perform its specific code-breaking tasks.3214