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

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.

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 (1^st generation Core I)
• Sandy Bridge (2^nd generation Core I)
• Ivy Bridge (3^rd generation Core I)
• Haswel (4^th generation Core I)
• Broadwell (5^th generation Core I)
• Skylake (6^th generation Core I)
• Kaby Lake (7^th generation Core I)
• Coffee Lake (8^th generation Core I)
• Coffee Lake Refresh (9^th generation Core I)
• Ice Lake (10^th generation Core I)
• Rocket Lake (11^th generation Core I)
• Alder Lake (12^th 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

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.

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.

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.