Early computers | IT orientational training

What is a computer? – Early computers

Early computers were meant to be used only for ~~calculations~~. Simple ~~manual~~ instruments like the abacus have aided people in doing calculations since ancient times. Early in the Industrial Revolution, some ~~mechanical~~ devices were built to automate long, tedious tasks, such as guiding patterns for looms. More sophisticated electrical or ~~electromechanical~~ machines (e.g. Konrad Zuse's Z3) did specialized analog or digital calculations in the early 20th century. The first digital^* ~~electronic~~^* calculating machines were developed during World War II. The first programmable, electronic, general-purpose digital computer was the famous ~~ENIAC~~ which was completed in 1945.
The vacuum tubes and the first discrete ~~semiconductor~~ components like diodes and bipolar transistors were followed by the silicon-based monolithic integrated circuit or chip technologies in the late 1950s. Integrated circuits were integrating a gradually increasing number of tiny transistors into one single semiconductor ~~chip~~. This gradually lead to the development of the microprocessor and in turn the ~~microcomputer~~ revolution in the 1970s. The speed, power and versatility of ~~computers~~^* have been increasing dramatically ever since then, with ~~transistor~~ counts increasing at a rapid pace (as predicted by Moore's law). Along with the rapid development of wide-area computer ~~networks~~^* like the Internet, this lead to the Digital Revolution during the late 20th to early 21st centuries.^⇒

What does electronic mean?
The main hardware units of an electronic computer (e.g. the central unit, the motherboard, extension cards etc.) consist of electronic components for the most part, such as resistors, capacitors, diodes, transistors, integrated circuits etc.

A transistor is a semiconductor device which is one of the basic building blocks of modern electronics. Because the transistor can be used as an electronic switch to open or close the controlled circuit in response to a control signal, it is an ideal tool for implementing logic gates and circuits.
An integrated circuit (IC) is a set of electronic circuits on one small flat piece or "chip" of semiconductor material (which is usually made of silicon). In this technology, large numbers of tiny transistors are integrated into a small chip. This results in circuits that are orders of magnitude smaller, faster, and less expensive than those constructed of discrete electronic components. Integrated circuits, having achieved very large-scale integration, are now used in virtually all electronic equipment and revolutionized the world of electronics.

Very large-scale integration (VLSI) is the technology of creating an integrated circuit by integrating millions of transistors into a single chip. For example, the microprocessor and the memory chips are VLSI devices. Today's microprocessors have many millions of logic gates and billions of individual transistors.

In terms of the logic functions and logical operations that electronic circuits technically implement, logic gates and circuits form the basis of how the computer works.

A logic gate is a device that implements an elementary logic function; accordingly, we can speak about AND, OR, NAND, NOR etc. gates. (The gates implementing the NOT function are called inverters.) In order to represent the two logic states, in electronic logic gates two different voltage levels are used for the input and output signals. Usually the high voltage level represents true, and the low voltage level represents false.
A logic circuit is a device that implements a complex logic function. It means that when receiving a specified binary input (that is, a certain combination of binary values), a logic circuit can produce a specified binary output. It is accomplished by several logic gates connected with each other to implement a given logic function (specified e.g. by a truth table). There are two different types of logic circuits:

In combinational circuits the output values are solely a function of the actual combination of the input values (and nothing else). For example, an adder is a combinational circuit.
In sequential circuits the output values are a function of both the actual combination of the input values and some preceding values or parameters that the circuit previously produced. Those parameters are called the states of the circuit which can be set by using feedbacks. For example, memory elements like flip-flops are sequential circuits.