IBM 650
IBM’s model 650, launched on the market in 1954, was the first computer sold on a large scale—over a thousand units—that opened the doors to a new digital era. Nicknamed the “magnetic drum calculator”, the IBM 650 featured a remarkable architecture for its time. Its heart beat to the rhythm of a nickel-cobalt rotating drum 10 centimeters in diameter and 40 centimeters in length. This cylinder rotated at the dizzying speed of 12,500 revolutions per minute and stored 2,000 “words” of ten digits. The particular arrangement of data in 40 bands of 50 positions forced programmers into constant mental gymnastics to minimize access times related to drum rotation.
The physical architecture of the system was divided into three distinct blocks: the central console housing the famous drum and arithmetic circuits, the read-punch unit (model 533) for data input and output, and the power supply unit (model 655) that transformed the language of punched cards into electronic signals comprehensible by the machine.
A technical peculiarity of the IBM 650 lay in its “one plus one address” instruction set. Each instruction contained the operation to be performed as well as the location of the next instruction. This approach, sometimes criticized by modern theorists, proved brilliant in the context of magnetic drum constraints. With only 44 operation codes available, the machine forced economy and elegance in program writing. Donald Knuth, who began programming on this machine during his studies, retained throughout his life a particular fondness for this simplicity that stimulated inventiveness.
The machine evolved and the 653 system enriched the initial configuration with index registers, a floating-point calculation unit, and 60 words of fast memory. Additional peripherals such as magnetic tapes and printers gradually completed the 650 ecosystem, extending its capabilities while maintaining compatibility with existing programs.
The software aspect underwent equally rich development. The SOAP (Symbolic Optimal Assembly Program) assembler created by Stan Poley freed programmers from direct machine code programming. The Bell Labs interpreter, the work of Wolontis, considerably facilitated scientific calculations through floating-point arithmetic. An extensive library of over 200 programs emerged, covering domains as varied as pure mathematics, statistics, management, or solving differential equations.
At Carnegie Tech (now Carnegie Mellon), Herbert Simon and Allen Newell developed on the IBM 650 their IPL-V (Information Processing Language), a precursor in the field of artificial intelligence. This list-processing language introduced determining concepts such as top-down programming and closed subroutines—principles that later became fundamentals of structured programming.
The robustness and relative accessibility of the IBM 650 transformed it into an unparalleled educational tool. Unlike its contemporaries that required highly specialized personnel, this machine could be used directly by students and researchers. Thousands of programmers cut their teeth on its consoles, forming the first massive generation of computing professionals.
The technical limitations of the machine—restricted memory and variable drum access times—proved paradoxically fertile. They forced programmers to develop sophisticated optimization techniques and to think about the structure of their algorithms. These practices durably influenced the teaching and design of computer programs up to the present day.
Beyond technical specifications, the IBM 650 represents the moment when computing left the laboratories to enter offices and universities. It was no longer an experimental curiosity but a practical, reliable, and relatively accessible tool.