Central processing unit

The central processing unit emerged because the von Neumann architecture required a single component to execute the instructions stored in memory. On June 21, 1948, at the University of Manchester, the Small Scale Experimental Machine—nicknamed 'Baby'—became the first computer to run a program stored in electronic memory, and in doing so, demonstrated the first true CPU.

The intellectual foundation came from John von Neumann's 1945 'First Draft of a Report on the EDVAC,' which described a computer architecture with distinct components: a processing unit containing an arithmetic-logic unit (ALU), a control unit that interprets instructions, and memory that stores both data and the program itself. This architecture—developed in discussions with ENIAC creators John Mauchly and J. Presper Eckert at the University of Pennsylvania's Moore School—would define computing for decades.

But von Neumann's design was theoretical. The practical construction required a suitable memory device. The Manchester team, led by Frederic Williams and Tom Kilburn, solved this with the Williams tube—an early form of computer memory using a standard cathode-ray tube to store bits as electrostatic charges. With working memory in hand, they could build a machine that truly separated program from hardware.

The Baby's first program—just 17 instructions—was written by Kilburn to find the highest proper factor of a given number. On that June day in 1948, the machine successfully factored 2^18 (262,144) in 52 minutes. As one historian noted: 'That was the first time, anywhere in the world, that a program stored in an electronic memory was executed and completed.'

The Manchester Mark 1, Baby's successor, went operational in 1949 and was commercialized by Ferranti as the Ferranti Mark 1 in 1951—the world's first commercially available general-purpose electronic computer. The CPU design that emerged from Manchester became the template: fetch an instruction from memory, decode it, execute it, store the result, repeat.

What made the CPU conceptually distinct was unification. Earlier computing machines had separate mechanisms for different operations. The CPU consolidated arithmetic, logic, and control into a single unit that could perform any computation by following stored instructions. The hardware became general-purpose; specificity moved to software.

The von Neumann architecture's influence proved so complete that nearly all common CPUs today—from smartphone chips to supercomputer processors—remain fundamentally von Neumann stored-program machines. The basic design and function established in 1948 has not changed much, even as complexity, size, and speed have transformed beyond recognition. A modern CPU contains billions of transistors executing billions of instructions per second, but the conceptual model remains: fetch, decode, execute, store. The Manchester Baby established a pattern that computing has never escaped.