What is a CPU? How is CPU classified and how it works?

This post is lesson 26 of 42 in the subject Computer Hardware

1. What is CPU? Function of CPU

CPU (Central Processing Unit) also called microprocessor or processor. It is known as the brain of the computer. CPU is a complex integrated circuit consisting of millions of transistors.

CPU (Central Processing Unit) 

Computer has the function of executing the program. A program consists of a sequence of instructions stored in memory. CPU undertakes this execution.

The program execution process consists of two steps:

  • CPU reads instructions from memory
  • CPU executes that instruction

Program execution is the repetition of reading instructions and executing instructions.

2. History of CPU

The first commercial CPU was Intel 4004 from Intel manufacturer. It is introduced by Intel in November 1971. Intel 4004 had 2250 transistors and 16 pins.


Then, the widely used microprocessor was the Intel 8080, born in 1974.

In 2006, Intel introduced Intel Northwood Pentium microprocessor, which had 55 million transistors and 478 pins.

CPUs of Intel in 1971 had only 2250 transistors, until 2016, they had 7.2 billion transistors with 22 cores thanks to 14 nm lithography process.


A well-known law in CPU manufacturing is Moore’s law: “The number of transistors per square inch will double every 24 months.” (1 square inch is approximately 6.45 cm²).

When we cannot reduce size of a transistor further, Moore’s law will no longer right.

3. How is CPU classified?

3.1. Classified by CPU’s microarchitecture

Based on microarchitecture, CPUs are classified into many types:

  • Netburst: Willamette, Northwood, Prescott
  • P6M/Banias: Banias, Dothan, Dothan533, Yonah
  • Core/Penryn: Conroe, Wolfdale, Kentsfield, Yorkfield
  • Nehalem (1st generation Core I)
  • Sandy Bridge (2nd generation Core I)
  • Ivy Bridge (3rd generation Core I)
  • Haswel (4th generation Core I)
  • Broadwell (5th generation Core I)
  • Skylake (6th generation Core I)
  • Kaby Lake (7th generation Core I)
  • Coffee Lake (8th generation Core I)
  • Coffee Lake Refresh (9th generation Core I)
  • Ice Lake (10th generation Core I)
  • Rocket Lake (11th generation Core I)
  • Alder Lake (12th generation Core I)

3.2. Classified by semiconductor manufacturing process nodes in CPU

It is mainly based on transistor scaling. They are methods of reducing size of each transistor in CPU. There are semiconductor manufacturing process nodes in CPU such as 130nm/90nm/65nm/45nm/32nm/22nm/14nm/7nm/4nm, etc.

3.3. Classified by purpose of use

Each CPU is built for different uses:

  • CPU for mobiles
  • CPUs for desktops
  • CPU for workstations, servers

CPU Intel Xeon for server

4. Working principle of CPU

When computer is running a program, program’s instructions will be loaded into RAM memory. CPU will read and follow instructions one after the other.

During reading and following instructions, decoder will decode these instructions into control signals.

Operation of CPU

5. CPU manufacturers

Intel and AMD are the two largest CPU manufacturers on the market today.

Intel CPU series

  • Intel® Core™, Intel® Pentium®, Intel® Celeron® CPU family for Desktops, Laptops and Notebooks.
  • Intel® Xeon™, Intel® Itanium™ CPU family for servers, workstations.
Intel Celeron

AMD CPU series

  • Phenom™, Athlon™, Sempron™ CPU family for Desktop.
  • Turion™ 64X2 Dual-Core mobile technology microprocessor family, Athlon 64X2, Mobile AMD Sempron CPU family for Laptop, Notebook.
  • Athlon MP, Opteron™ CPU family for servers, workstations.
CPU AMD Athlon X2
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Posted by Vinh Le

Composer at ITLearningCorner.

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