• 1st Gen (1940s–50s): vacuum tubes, machine language, huge/slow/hot (e.g., ENIAC)
• 2nd Gen (1950s–60s): transistors — smaller, faster, less heat; assembly language emerges
• 3rd Gen (1960s–70s): Integrated Circuits (ICs) — multiple transistors on a chip; high-level languages (COBOL, FORTRAN)
• 4th Gen (1970s–present): microprocessors (VLSI) — the entire CPU on one chip (e.g., Intel 4004, 1971); personal computers emerge
• 5th Gen (emerging): AI-based computing, parallel processing, natural language interfaces

Detailed Timeline (Book Notes — Key Named Milestones)

Exam angle: examiners like to test who invented what, and when — this timeline gives you the names to attach to each device.

Pre-electronic / Early Mechanical Era

• 1642 — Pascaline: mechanical calculator built by Blaise Pascal (the Pascal programming language is named after him)
• 1804 — Jacquard Loom: a loom programmed using punched cards, invented by Joseph Marie Jacquard — punched cards later became central to early computing input/programming
• ca. 1837–1850 — Difference Engine / Analytical Engine: designed by Charles Babbage with Ada Byron (Lovelace) — Babbage's hand-cranked, mechanical Analytical Engine anticipated virtually every aspect of a modern computer over 100 years before one was actually built; Ada Lovelace is credited with writing the first algorithm intended for a machine

Early Electronic Computers (1930s–1940s)

• 1936 — Z1 Computer: built by Konrad Zuse — the first freely programmable computer
• 1939–1942 — Atanasoff-Berry Computer (ABC): built by Prof. John V. Atanasoff and graduate student Clifford Berry at Iowa State — represented several "firsts": binary arithmetic, parallel processing, regenerative memory, and separation of memory from computing functions; weighed 750 lbs, stored 3,000 bits (0.4K)
• 1940s — Colossus: a vacuum-tube computing machine that broke Hitler's codes in WWII, built by codebreakers at Bletchley Park, England (associated with Alan Turing) — shortened the war and is considered instrumental to the Allied codebreaking effort
• 1944 — Harvard Mark I: built by Howard Aiken and Grace Hopper
• 1946 — ENIAC: World's first electronic, large-scale, general-purpose computer, built by J. Presper Eckert and John W. Mauchly at the University of Pennsylvania — a 30-ton machine, 50×30 feet, 19,000 vacuum tubes, 6,000 switches, could add 5,000 numbers/second; had no software — reprogramming meant physically rewiring it; used for H-bomb calculations and artillery trajectory tables
• 1947/48 — The Transistor: invented by John Bardeen, Walter Brattain, and William Shockley — not a computer itself, but the single invention that most transformed computing history (replaced vacuum tubes)
• 1948 — Manchester Baby Computer & the Williams Tube: built by Frederic Williams and Tom Kilburn

Commercial Computing Era (1950s–1960s)