Instruction Cycle and I/O Operations in Basic Computer Architecture

Explore the fundamental instruction cycle and input/output (I/O) operations in a basic computer. This guide details the steps involved in fetching and executing instructions, and explains how I/O devices interact with the CPU and memory, providing a foundational understanding of computer operation.

Instruction Cycle and Input/Output in a Basic Computer

The Instruction Cycle

A computer executes a program by fetching and executing instructions one at a time. This process, called the instruction cycle, typically involves several steps.

Phases of the Instruction Cycle

  1. Fetch: The next instruction is fetched from memory.
  2. Decode: The instruction is decoded to determine the operation to perform and the operands involved.
  3. Read Effective Address: The memory address of any operands needed is calculated. Different addressing modes are used to calculate the actual address of the data to be used or written.
  4. Execute: The operation specified by the instruction is performed.

Input/Output (I/O) Configuration

I/O devices enable the computer to interact with the outside world. Input devices provide data to the computer (e.g., a keyboard), and output devices display results (e.g., a printer).

I/O System Block Diagram

(A block diagram illustrating the I/O configuration of a basic computer should be included here. The diagram should clearly show the input-output terminals, input register (INPR), output register (OUTR), transmitter interface, receiver interface, and accumulator (AC). The details of communication between the components should be included in the description.)

Components of a Basic Computer

A basic computer comprises several key hardware components:

  • Memory Unit: Stores instructions and data. (e.g., 4096 words of 16 bits each)
  • Registers: High-speed storage locations within the CPU. (Examples include: AC (Accumulator), DR (Data Register), AR (Address Register), IR (Instruction Register), PC (Program Counter), TR (Temporary Register), SC (Sequence Counter), INPR (Input Register), OUTR (Output Register).
  • Flip-Flops: Basic memory elements that store individual bits of information. (Examples: I, S, E, R, IEN, FGI, FGO, where FGI and FGO are input and output flags).
  • Decoders: Circuits that translate instructions into control signals. (Examples: Operation decoder (3x8) and Timing decoder (4x16)).
  • Common Bus: A shared pathway for data transfer between components.
  • Control Logic Gates and Arithmetic Logic Unit (ALU): Used to execute instructions.

Conclusion

This section provides an overview of the instruction cycle and input/output mechanisms within a simplified computer architecture. Understanding this foundational architecture helps in appreciating the complexities of modern computer systems.