Generations of Microprocessor

The transistor technology led to the introduction of minicomputers of the 1960s and the personal computer revolution of the 1970s.

Microprocessors evolution is categorized into 5 generations i.e. first, second, third, fourth, and fifth generations.

Working of a Microprocessor

There are three steps that a microprocessor follows –

1. Fetch – The instructions are in storage from where the processor fetches them.

2. Decode – It then decodes the instruction to assign the task further. During this, the arithmetic and logic unit also performs to register the data temporarily. 

3. Execute – The assigned tasks undergo execution and reach the output port in binary form. 

Block Diagram of a Microprocessor

Arithmetic and Logical Unit, Control Unit, and Register array make up the microprocessor. The ALU deals with input devices or memory for receiving data. The control unit takes care of instructions and structure. Register array identifies and saves the registers like B, C, and accumulator.

Block Diagram of a Microprocessor

Basic Microprocessor Terms

  • Instructions Per Cycle – A way to measure CPU’s instruction speed in a single clock.
  • Instruction Set – These are the commands that a processor understands to work between hardware and software.
  • Bus – Set of conductors for data transmission, information control, and tasks addressed in a microprocessor. They are of three types – data bus, address bus, and control bus.
  • Word Length – Refers to the number of bits processed at a time. 
  • Clock Speed / Clock Rate – The ability of microprocessors to perform tasks in a second. 
  • Bandwidth – Refers to the total bits in a single instruction.
  • Data Types – Data type microprocessor supports like binary, ASCII, etc.
  • SIMD – Single Instruction Multiple Data
  • PGA – Pin Grid Array
  • FPU – Floating Point Unit
  • ALU – Arithmetic and Logic Unit
  • MMX – MultiMedia eXtensions
  • MMU – Memory Management Unit

Evolution of Microprocessors

1. First Generation – 4bit Microprocessors

The Intel corporation came out with the first generation of microprocessors in 1971. They were 4-bit processors namely Intel 4004. The speed of the processor was 740 kHz taking 60k instructions per second. It had 2300 transistors and 16 pins inside.

Built on a single chip, it was useful for simple arithmetic and logical operations. A control unit was there to understand the instructions from memory and execute the tasks.

2. Second Generation – 8bit Microprocessor

The second generation began in 1973 by Intel as the first 8 – bit microprocessor. It was useful for arithmetic and logic operations on 8-bit words. The first processor was 8008 with a clock speed of 500kHz and 50k instructions per second.

Followed by an 8080 microprocessor in 1974 with a speed of 2 MHz and 60k instruction per second. Lastly came the 8085 microprocessor in 1976 having an ability of 769230 instruction per second with 3 MHz speed.

3. Third Generation – 16bit Microprocessor

The third generation began with 8086-88 microprocessors in 1978 with 4.77, 8 & 10 MHz speed and 2.5 million instructions per second. Other important inventions were Zilog Z800, and 80286, which came out in 1982 and could read 4 million instructions per second with 68 pins inside.

4. Fourth Generation – 32bit Microprocessors

Intel was still the leader as many companies came out with 32-bit microprocessors around 1986. Their clock speed was between 16 MHz to 33 MHz with 275k transistors inside.

One of the first ones was the Intel 80486 microprocessor of 1986 with 16-100MHz clock speed and 1.2 Million transistors with 8 KB of cache memory. Followed by the PENTIUM microprocessor in 1993 which had 66 MHz clock speed and 8-bit of cache memory.

5. Fifth Generation – 64bit Microprocessors

Began in 1995, the Pentium processor was one of the first 64-bit processors with 1.2 GHz to 3 GHz clock speed. There were 291 Million transistors and 64kb instruction per second.

Followed by i3, i5, i7 microprocessors in 2007, 2009, 2010 respectively. These were some of the key points of this generation.

About Pentium Series

Instead of 80586 Intel came out with new processor namely “Pentium” Processor. It’s performance is closer to “RISC” performance. Pentium was followed by “Pentium Pro” CPU.

Pentium pro allow multiple CPU in a system in order to achieve multiprocessing.

Important Intel Processors

NameYearData WidthClock Speed
Pentium Pro199532-bit150-200MHz
Pentium II199764-bit233MHz
Pentium III199964-bit450MHz

Advantages of Microprocessors

  • High-speed processing
  • Brings intelligence to the system
  • Is flexible in nature
  • Has a compact size
  • Is easy to maintain

Disadvantages of Microprocessors

  • Leads to overheating due to continuous use.  
  • The data size decides the performance
  • Larger than microcontrollers  
  • Doesn’t support floating-point operations 

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