Basic Operational Concepts of a Computer System: Understanding Hardware and Software Interaction

This guide provides a foundational understanding of how computer systems operate, explaining the roles of the CPU, memory, input/output (I/O) devices, and the processes involved in executing instructions. It also explores methods of I/O management (polling, interrupts).

Basic Operational Concepts of a Computer System

Instruction Execution

A computer executes a program, which is a sequence of instructions stored in the computer's memory. The CPU (Central Processing Unit) fetches these instructions one by one and executes them. Data needed for the instructions are typically also stored in memory.

Components Involved in Instruction Execution

Several components within a computer work together to execute an instruction:

  • Arithmetic Logic Unit (ALU): Performs arithmetic and logical operations.
  • Control Unit: Directs the execution of instructions.
  • Registers: High-speed storage locations within the CPU used to hold data and instructions temporarily (e.g., Program Counter, Instruction Register, Memory Address Register, Memory Data Register).

Key Registers

  • Program Counter (PC): Stores the address of the next instruction to be fetched.
  • Instruction Register (IR): Holds the current instruction being executed.
  • Memory Address Register (MAR): Holds the address of the memory location to be accessed.
  • Memory Data Register (MDR): Holds the data being transferred to or from memory.

Input/Output (I/O) Device Servicing

The CPU interacts with external devices (like keyboards and printers) using I/O operations. Two main ways exist for the CPU to manage these operations:

1. Polling

Polling involves the CPU periodically checking the status of I/O devices to determine if they need service. It is simple but can be inefficient, as the CPU wastes time polling devices that don't need attention.

2. Interrupts

An interrupt is a signal from an I/O device indicating that it requires service. The interrupt causes the CPU to suspend its current task and execute an interrupt service routine (ISR) to handle the device's request. This is generally more efficient than polling because the CPU only handles I/O when needed.

Conclusion

This section outlines the basic operational concepts of a computer—instruction execution, memory access, and I/O operations. These processes work in concert, orchestrated by the CPU's control unit, to make a computer function.