Note on Microprocessor

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Graphic image of Microprocessor

Fig: Microprocessor

The microprocessor is an entire CPU built on a single chip. To elaborate, it is a computer processor which embodies the functions of a CPU on a single IC or at most a few Integrated Circuits. Integrated Circuits are very complex electronic circuits which consist of extremely tiny components that are formed on a single, flat, thin piece of material known as Semiconductor. In other words, microprocessor isan integrated circuit that contains all the functions of a central processing unit of a computer.A microprocessor is designed to perform arithmetic and logic operations that make use of small number-holding areas called registers.


Fig: Microprocessor


The microprocessor is an electronic device which is attached to the main circuit board (motherboard) of a microcomputer which serves as the brain of the computer. It is linked with various peripheral equipment such as main memory, input/output devices and auxiliary storage devices, etc.

Before microprocessors, computers had Small Scale Integration (SSI) and Medium Scale Integration (MSI) chips. Though 3 companies; Intel Corporation, Garret Air Research and Texas Instruments, all developed the microprocessors at around the same time, Intel Corporation’s microprocessor is considered to be the 1st one as the Intel 4004 microprocessor. Conceived the idea in 1968, this single chip was brought into reality in November 1971 as the very 1st commercial microprocessor.


Fig: Microprocessor


Intel 4004 by Intel Corporation

The Intel 4004 ("four-thousand-four") is a 4-bit central processing unit (CPU) released by Intel Corporation, in 1971. It was the first microprocessor as well as the first general purpose programmable microprocessor on the market.

Fig:Intel 4004 by Intel Corporation
Intel 8008 by Intel Corporation

The very next year in 1972, Intel Corporation again released a more advanced microprocessor called Intel 8008 as the 1st 8-bit microprocessor.It was an 8-bit CPU with an external 14-bit address bus that could address 16 KB of memory.

The 8008 had other advantages over the 4004:

  • The processor supported of 16 KB of memory (ROM and RAM combined).
  • The size of internal CPU stack was 7 levels in contrast to 3 level-stack for the i4004.
  • The Intel 8008 could handle interrupts.
Fig:Intel 8008 by Intel corporation


A microprocessor is often referred to as the CPU or Central Processing Unit. It is considered to be the heart of a computer as it controls all the functions of a computer. It can be considered as an artificial brain. This system can control everything from large automobiles to small devices, such as mobile phones and calculators.

Fig: Components of Microprocessor
Fig: Components of Microprocessor

But, a microprocessor alone does not have any meaning unless and until it is attached to other components of a digital computer. It consists of several sections. The Arithmetic/Logic Unit (ALU) performs calculations and makes logical decisions; the Control Unit deciphers programs; digital information is carried by Buses throughout the computer and the chip; the registers store temporary information like a scratch pad does and on-chip computation is supported by local memory.

There are some more complex microprocessors too, which contains some extra sections like Cache Memory for the storage of specialized memory and to speed up access for external data storage devices. Generally, though, it consists of 3 major components. They are:

  • ALU
  • CU
  • Register Array

ALU (Arithmetic and Logic unit): This is the area of the microprocessor where various computing functions are performed on data. The ALU performs arithmetic operations such as addition, subtraction, multiplication and division and logical operations such as AND, OR and NOT .The result of the operation is stored in the registers called Accumulator. ALU also performs an operations like increment, decrement, shift and clear.
Fig: Arithmetic Logic Unit

Control Unit: The control unit provides the necessary timing and control signals to all the operation in the microcomputer. It is the one in charge of informing all the ALU units of what operations are to be performed on. Some of its features are:

  • It receives, decodes, stores the results and manages the execution of data that flows throughout the CPU.
  • It controls the flow of data between the microprocessor and memory and peripherals.
  • It also directs the Arithmetic and Logic Unit.
  • It generates the Control Output based on the input called Operation Code (Opcode) which can also be called as an Instruction.
  • It commands and controls the Program Unit which is responsible for giving away the data based on the addresses.
  • It supervises and controls the entire operation of a computer.
  • Based on the CPU, the functions that a Control Unit performs can be varied.
    Fig: Control Unit

Therefore, the ALU might be able to perform lots of its functions at a time but based on the Control Unit, it can perform only one operation at a time. It controls the flow of data between the microprocessor and memory and peripherals.

Register Array: Simply, it is a vital component of a computer which serves as the storage location that is inside the processor. This is the area of the microprocessor which consists of various registers. These registers are primarily used to store data temporarily during the execution of a program. It accepts, stores and transfers the data and instructions that are used immediately.

Memory Unit

Fig: Memory Unit


Memory Chips

Fig: Memory chips


These registers are very small memory locations which hold the data to be processed. The instruction pointer is known as the most important register that directs the CPU to the next location from where it has to receive data. The accumulator is another type of register which stores the next values to be processed by the CPU. The size of the register determines the overall speed of the computer.


The microprocessor is considered to be the heart and brain of a computer as it is responsible for the whole performance from directing every function within the computer. It can conduct any computation or operation accurately at the earliest due to floating point processors. With the incorporated effort of the ALU, Control Unit and Registers, microprocessor carries out the required instructions and duties efficiently. There are mainly 2 important memories that are responsible for any microprocessor to control and function. They are:

  1. ROM (Read Only Memory):

ROM is a program with a finite and fixed set of bytes and instructions. Within it, it has a small program called the Basic Input Output System or BIOS. It is a program which tests the hardware of the machine when it starts up. Then, it fetches a program called the boot sector from another memory which executes some instructions serially which helps in utilizing the computer efficiently.


  1. RAM (Random Access Memory):

RAM is a program which consists of pre-set number of bytes which can store a limited amount of information. Its set of bytes does not last long and is variable. On switched off, this memory is completely wiped off from the computer.


Fig: Random Access Memory


Together, these 2 memories constitute microprocessor and makes it work with efficiency. Without them, microprocessor possibly cannot perform any of its function properly. Among all the functions, some of them are given below in summary:

  • It obtains instruction from the main memory.
  • Then, the instruction is decoded in order to determine what action is to be done.
  • Based on the instructions’ nature or requirement, data and information are fetched from the main memory or input / output module.
  • With the help of logical and arithmetic calculation, the instruction is then executed.
  • Along with the execution of the instruction, it also controls and supervises the input / output devices.
  • If requested action gets interrupted from I/O devices, it suspends the current program's execution and transfers to its control to an interrupt handling program.
  • Finally, the instruction’s results may need to be transferred to memory or an I/O module, throughout which the microprocessor keeps performing its tasks.

(Rokka, Bhusal, & Manandhar, 2013)


Rokka, P., Bhusal, R., & Manandhar, S. (2013). Computer Essentials I. Putalisadak, Kathmandu: Asmita's Publication.

Definition of Microprocessor.

Components of microprocessor:

  • ALU (Arithmetic and Logic unit).
  • Control Unit.
  • Register Array.

Main memories of the microprocessor:

  • RAM(Random Access Memory).
  • ROM (Read Only Memory).

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