Modern computers have millions of transistors which form highly complex circuits that handle data. The latest microprocessor chipset by Intel (skylake core i7) has 1.7 Billion transistors. All the logical operations in a computer are held in the Arithmetic and Logical Unit (ALU) of the microprocessor. Today all the different sections of a CPU are fabricated in a single chip (called monolithic design). The Intel 4004 CPU was the first monolithic CPU.

Here is the circuit diagram of Intel 4004 which was released in 1971. Look how complex it is - but today’s CPUs are much more advanced. This picture-story by Intel shows how a CPU is made.

Moore’s Law is an observation by Gordon E Moore, the co–founder of Intel. It states that the number of transistors in a computer CPU doubles every two years.

For a computer to work, other systems are also needed, like memory, to store data. To really understand how a computer works, we have to learn how numbers are stored and processed and how the CPU and other systems interact. The first answer in this page gives a very brief idea. Here is a more detailed explanation.

Apart from the AND gate discussed in the lesson, there are many other logic gates. All logic gates are represented by symbols. This page lists all basic logic gates and how they can be made using transistors. Logic gates perform complex operations when combined or layered. The idea of circuit addition is explained here with the help of dominoes. And here is an example of a circuit that adds two binary numbers using logic gates.

The transistor was invented by John Bardeen, Walter Brattain and William Shockley at Bell labs, USA. Although the explanation in this video was quite simple, the transistor is actually a highly complex device. This tutorial explains the construction and principles of transistors. The type of transistor discussed in the lesson is called a Bipolar Junction Transistor or BJT. This transistor is actually not used in computer chips. Another type of transistor called CMOS (Complementary Metal Oxide Semiconductor) transistors are used in CPU chips. These are a sub-type of a more general category of transistors called MOSFETs (Metal Oxide Semiconductor Field Effect Transistor). Here is a brilliant video on how it works.