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Classification of computers

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Prerita Agarwal
Data Specialist @
23 Jul, 2024 @ 01:30 PM

Introduction

The computers we see today have evolved from a few basic concepts derived by people like us. It was not as advanced an idea back then but gave a kickstart to this digitised world. We will look at architecture concepts that paved the way or provided a basis for today’s super-advanced machines.

Classification of computers

There exist two major classifications of computers:

  1. Stored Program Control Concept
  2. Flynn’s Classification of Computers

Recommended Topic - Shift Registers in Digital Electronics and Difference Between Jfet and Mosfet

Stored Program Control Concept

This concept simply refers to storing the instructions to execute them in sequence. John Von Neumann introduced this idea in the late 1940s; he proposed that programs be stored electronically in binary format to modify instructions on repeated instruction executions. Electronic Numerical Integrator and Computer(ENIAC) is one of the examples that came up during the early 1940s.

Following are further classifications in the Stored Program Concept

  • Von-Neumann Model
  • General Purpose System
  • Parallel Processing

Von Neumann Model 

The computer achitecture design proposed by Von Neumann came in 1945 following the concept of stored program control. It consists of an Arithmetic and Logical memory unit(ALU), Registers. Control unit and input/output. Its working is based on a single processor, uses single memory for both instructions and data and does program execution using fetch, decode and execute cycle.

Following are components inside the von-Neumann model:

  1. Central processing unit
  2. Buses
  3. Memory unit

Let’s discuss each one in brief.

Central Processing unit

It processes all of the data operations coming from the instructions from the input/output. There are three significant components inside the CPU: arithmetic logic unit(ALU), Control Unit (CU), and Registers. ALU does all the micro-tasks relating to operations on the instructions, like arithmetic operations (addition, subtraction), logical operations (AND, OR, NOT). The Control Unit only controls the functions of ALU, memory, input and output. Registers contain high-speed storage separate from memory, used to prioritise data processing.

Below is the list of different types of registers.

Registers Descriptions
Memory Address Register Holds memory location of data needing to be held
Memory Data Register Holds data being transferred.
Program Counter Holds the address of the next instruction to be processed.
Accumulator Holds logical results
Current Instruction Register It has instructions currently being processed

Buses

It is a path to interchange information between registers. 

Bus Description
Databus It acts as a carrier of data between the processor, input/output and memory unit.
Address bus Contains addresses of data between memory and processor. These are addresses and not the data itself
Control bus It carries commands as well as signals coming from CPU

Memory Unit

It has storage cells bound together in the form of circuits responsible for storing data and feeding it to input/output and processors. 

You can also read about Input-Output Processor here.

It consists of two types:

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

General-purpose system 

It consists of ALU, Control units and processors which are interconnected by bus for purpose of exchange of information.

Also read, microprogrammed control unit

Parallel processing

It enables us to achieve multitasking by providing multiple data processing at the same time. Parallel processing systems provide the ability to perform multiple functions like addition, subtraction, increment, decrement at the same time.

Recommended topic: Cloud Computing

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Flynn’s classification of computers

Classification based on the number of instructions and data was proposed by MJ Flynn. The idea introduced two types of streams. The instruction stream included a continuous sequence of instructions that is read from memory and the data stream consists of operations performed on data.

There exists four subcategories:

  1. SISD(Single instruction stream, Single data stream)
  2. SIMD(Single instruction stream, Multiple data stream)
  3. MISD(Multiple instruction stream, Single data stream)
  4. MIMD (Multiple instruction stream, Multiple data stream)
     

Read about Instruction Format in Computer Architecture

Must Read hardwired and microprogrammed control unit, microprogrammed control unit

You can also read about - Memory hierarchy in computer network

FAQs

  1. What is a stream?
    The objects in a sequence that comes up to the CPU unit for the purpose of execution is termed as a stream. One can image a conveyer belt providing data from one place to another.
     
  2. What is an instruction stream?
    It refers to instructions provided to the central processing unit(CPU) for being executed. Instructions can come from input and output.
     
  3. What is a data stream?
    The elements which contain data and are output for executions performed on the data is a data stream. It consists of bits and bytes.
     
  4. What is a processor?
    It is responsible for all the logical tasks like additions, subtractions, incrementations and decrementations coming from the input or output. It is an integral part of any computer system.
     
  5. How do registers work?
    Registers are temporary storage inside of the CPU. Data operations coming to the CPU are temporarily located at registers and results are provided directly from here without needing to store in permanent memory.

Key Takeaways

Congratulations on getting through this article on the classification of computers. We saw different classifications in computer architecture. We also discussed each of the subcategories. Now we have an idea of the concepts behind system architecture. 

To learn more about Micro Operations, refer to Arithmetic Micro Operations.

Take a look at our Guided paths on Coding Ninjas Studio to learn more about DSA, Competitive Programming, JavaScript, System Design, etc.

Happy Learning!

Topics covered
1.
Introduction
1.1.
Classification of computers
2.
Stored Program Control Concept
2.1.
Von Neumann Model 
2.1.1.
Central Processing unit
2.1.2.
Buses
2.1.3.
Memory Unit
2.2.
General-purpose system 
2.3.
Parallel processing
3.
Flynn’s classification of computers
4.
FAQs
5.
Key Takeaways