The 1940s produced the first computers built from electronics rather than gears and relays. Within a few years those machines gained the one feature that defines a modern computer: the stored program, instructions held in memory rather than wired into the machine.
The idea
A stored-program computer keeps its instructions in the same memory as its data. You redirect it by loading new instructions, not by rewiring it, which is what makes a single machine able to run any program.
Electronic, but not yet stored-program
Colossus, built by British codebreakers at Bletchley Park between 1943 and 1945, is regarded as the world’s first programmable electronic digital computer. It was built to break the German Lorenz cipher, not Enigma, which was the job of the earlier electromechanical Bombe. Across the Atlantic, ENIAC (1945) was general-purpose but was programmed by plugboard wiring and switches. Both machines were electronic, and neither yet held its program in memory.
The stored-program leap
The decisive step was to store the program in memory alongside the data, the idea at the heart of the von Neumann architecture. The Manchester Baby ran the first such program on 21 June 1948. It was a tiny machine built to prove a point, and the point was the most important one in computing: the modern computer’s defining feature worked.
Why it matters
Every general-purpose computer since is a stored-program electronic machine. Colossus and ENIAC proved that electronics could compute; the Baby proved the architecture that organizes how they compute. The people who programmed ENIAC were doing by plugboard what the stored program would soon let software do in memory.
Related Notes
- Von Neumann Architecture, the stored-program model these machines reached
- Ballistics Tables and ENIAC, the American general-purpose machine
- The ENIAC Programmers, who programmed it by hand
- Magnetic Disk Storage, the storage that came next
- History of Computing, the section index
Sources
- “Colossus computer,” Wikipedia. https://en.wikipedia.org/wiki/Colossus_computer . Supports Colossus as a British codebreaking machine of 1943-1945 regarded as the world’s first programmable electronic digital computer, used against the Lorenz cipher rather than Enigma.
- “Manchester Baby,” Wikipedia. https://en.wikipedia.org/wiki/Manchester_Baby . Supports the Baby as the first electronic stored-program computer, running its first program on 21 June 1948, and the stored-program concept of holding program and data in the same memory.