Instruction Cycle Quiz & Flashcards in Computer Architecture

Study Notes

Instruction Cycle Overview

A single cycle of operation, known as the instruction cycle, includes phases: Fetch, Decode, Execute, Memory Access, and Write Back.
An instruction describes an operation and its data operand locations.
A 32-bit word typically represents one encoded instruction.
Programs are sequences of instructions executed sequentially, with both programs and data stored in main memory.

Instruction Types

Load: Retrieves a data operand from memory or an input device to the processor.
Store: Transfers a data operand from a processor register to memory or an output device.
Operate: Executes arithmetic or logic operations on data operands within processor registers.

Example of a Simple Program

Labels A, B, and C represent memory addresses; Ri denotes processor registers.
Program for C = A + B involves:
- Load R2, A - Load value from address A into register R2.
- Load R3, B - Load value from address B into register R3.
- Add R4, R2, R3 - Add values in R2 and R3, storing the result in R4.
- Store R4, C - Store the result from R4 into address C.

Processor Components

The Program Counter (PC) holds the address of the current instruction and increments after each fetch.
The Instruction Register (IR) stores the current instruction being executed.
General-purpose registers are used to hold both data and addresses.
Control circuits and the Arithmetic and Logic Unit (ALU) are responsible for fetching and executing instructions.

Fetching and Executing Instructions

Example instruction: Load R2, LOC
Processor actions:
- Send PC address to memory and issue a Read command.
- Load instruction from memory into the IR and increment the PC.
- Send address LOC to memory, issuing a Read command to load data into R2.

Handling I/O Devices

An application program can:
- Read data from input devices (e.g., keyboard).
- Write data to output devices (e.g., display screen).
- Assess the readiness of I/O devices for data transfer.

Performance Considerations

Program execution speed is influenced by:
- Speed of electronic circuits within the processor.
- Access times for cache and main memory.
- Design efficiency of the instruction set.
- Ability to conduct multiple operations simultaneously (parallelism).

Technology Advancements

Improved materials for transistors lead to faster instruction execution.
Enhanced process technology facilitates placing more transistors on a chip, resulting in:
- Increased logic functionality.
- Greater memory storage capacity.

Performance - Parallelism

Multicore processors facilitate multiple processing units on a single chip.
Each core can operate independently, enhancing overall processing power.
Terms like dual-core, quad-core, and octo-core refer to the number of cores on the chip.

CPU Selection Considerations

For building a fast CPU computer, ensure the motherboard supports the required CPU socket type.

Description

Test your understanding of the instruction cycle, including fetch, decode, execute, memory access, and write back phases. Learn how instructions specify operations and data operands, and how they are stored and executed in the main memory.