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First electronic computers used vacuum tubes, and they were huge and complex.It was programmed using plugboards and switches, supporting input from an IBM card reader, and output to an IBM card punch. It took up 167 square meters, weighed 27 tons, and consuming 150 kilowatts of power
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The second generation of computers came about thanks to the invention of the transistor, which then started replacing vacuum tubes in computer design. Transistor computers consumed far less power, produced far less heat, and were much smaller compared to the first generation, albeit still big by today’s standards.
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Making circuits out of single pieces of silicon, which is a semiconductor, allowed them to be much smaller and more practical to produce. This also started the ongoing process of integrating an ever larger number of transistors onto a single microchip.
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First microchips-based central processing units consisted of multiple microchips for different CPU components. The drive for ever greater integration and miniaturization led towards single-chip CPUs, where all of the necessary CPU components were put onto a single microchip, called a microprocessor. The first single-chip CPU, or a microprocessor, was Intel 4004.
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First microcomputers were a weird bunch. They often came in kits, and many were essentially just boxes with lights and switches, usable only to engineers and hobbyists whom could understand binary code. Some, however, did come with a keyboard and/or a monitor, bearing somewhat more resemblance to modern computers.
