The evolution of computer technology is often divided into five generations.

Five Generations of Computers
Generations of computers	Generations timeline	Evolving hardware
First generation	1940s-1950s	Vacuum tube based
Second generation	1950s-1960s	Transistor based
Third generation	1960s-1970s	Integrated circuit based
Fourth generation	1970s-present	Microprocessor based
Fifth generation	The present and the future	Artificial intelligence based

The main characteristics of first generation of computers (1940s-1950s)

Main electronic component – vacuum tube
Main memory – magnetic drums and magnetic tapes
Programming language – machine language
Power – consume a lot of electricity and generate a lot of heat.
Speed and size – very slow and very large in size (often taking up entire room).
Input/output devices – punched cards and paper tape.
Examples – ENIAC, UNIVAC1, IBM 650, IBM 701, etc.
Quantity – there were about 100 different vacuum tube computers produced between 1942 and1963.

Second Generation of Computers

Main electronic component – transistor
Memory – magnetic core and magnetic tape / disk
Programming language – assembly language
Power and size – low power consumption, generated less heat, and smaller in size (in comparison with the first generation computers).
Speed – improvement of speed and reliability (in comparison with the first generation computers).
Input/output devices – punched cards and magnetic tape.
Examples – IBM 1401, IBM 7090 and 7094, UNIVAC 1107, etc.

Main electronic component – integrated circuits (ICs)
Memory – large magnetic core, magnetic tape / disk
Programming language – high level language (FORTRAN, BASIC, Pascal, COBOL, C, etc.)
Size – smaller, cheaper, and more efficient than second generation computers (they were called minicomputers).
Speed – improvement of speed and reliability (in comparison with the second generation computers).
Input / output devices – magnetic tape, keyboard, monitor, printer, etc.
Examples – IBM 360, IBM 370, PDP-11, UNIVAC 1108, etc.

Main electronic component – very large-scale integration (VLSI) and microprocessor.
VLSI– thousands of transistors on a single microchip.
Memory – semiconductor memory (such as RAM, ROM, etc.)
- RAM (random-access memory) – a type of data storage (memory element) used in computers that temporary stores of programs and data (volatile: its contents are lost when the computer is turned off).
- ROM (read-only memory) – a type of data storage used in computers that permanently stores data and programs (non-volatile: its contents are retained even when the computer is turned off).
Programming language – high level language (Python, C#, Java, JavaScript, Rust, Kotlin, etc.).
- A mix of both third- and fourth-generation languages
Size – smaller, cheaper and more efficient than third generation computers.
Speed – improvement of speed, accuracy, and reliability (in comparison with the third generation computers).
Input / output devices – keyboard, pointing devices, optical scanning, monitor, printer, etc.

Main electronic component: based on artificial intelligence, uses the Ultra Large-Scale Integration (ULSI) technology and parallel processing method.
- ULSI – millions of transistors on a single microchip
- Parallel processing method – use two or more microprocessors to run tasks simultaneously.
Language – understand natural language (human language).
Power – consume less power and generate less heat.
Speed – remarkable improvement of speed, accuracy and reliability (in comparison with the fourth generation computers).
Size – portable and small in size, and have a huge storage capacity.
Input / output device – keyboard, monitor, mouse, trackpad (or touchpad), touchscreen, pen, speech input (recognise voice / speech), light scanner, printer, etc.
Example – desktops, laptops, tablets, smartphones, etc.

Source: https://opentextbc.ca/computerstudies/chapter/classification-of-generations-of-computers/