CPU Fundamentals and Architecture

Overview

This lecture covers CPU fundamentals, factors affecting CPU performance, embedded systems, main CPU components, and the Von Neumann architecture.

CPU stands for Central Processing Unit, not Computer.
The CPU performs the Fetch, Decode, Execute (FDE) cycle billions of times per second.
Instructions come from input devices or running programs, fetched from RAM (also called main memory).
The FDE cycle: CPU fetches instruction from RAM, decodes it, then executes it.

Three main factors affect CPU performance: Clock Speed, Cores, and Cache (“the three C’s”).
Clock speed (measured in hertz, usually gigahertz) is instructions per second; higher clock speed = more FDE cycles per second.
Each core in a CPU can work independently; more cores = more instructions processed in parallel.
Example: 3.2 GHz dual core processes 6.4 billion instructions/sec; 3.5 GHz quad core does 14 billion instructions/sec.
Cache stores frequently used instructions; faster access than main memory but too much cache can decrease performance.

A computer is a programmable machine that processes data using the input-process-output model and is general purpose.
An embedded system is built into a larger machine, designed for one specific purpose, and usually doesn't need updating.
All components of an embedded system are typically on a single circuit board.
Examples: washing machines, microwaves, toasters, calculators.

The CPU has three main parts: Control Unit (CU), Arithmetic and Logic Unit (ALU), and Cache.
The Control Unit manages the FDE cycle and data movement within the CPU and memory.
The ALU performs calculations and logic operations (AND, OR, NOT).
The accumulator (part of the ALU) stores calculation results.
Cache stores frequently used instructions; divided into Level 1 (fastest, smallest), Level 2, and Level 3 (slowest, largest).

In Von Neumann architecture, the CPU runs programs stored in main memory (RAM).
Registers involved include: Program Counter (tracks current instruction), Memory Address Register (stores address to fetch), Memory Data Register (stores fetched data), and Accumulator (stores results).
The FDE cycle is supported by these registers: fetch instruction (address from PC), store data in MDR, decode, and execute via CU and ALU, repeat.

CPU — Central Processing Unit.
FDE Cycle — Fetch, Decode, Execute process carried out by the CPU.
RAM/Main Memory — Temporary storage for running instructions and data.
Clock Speed — Number of instructions processed per second (measured in hertz).
Core — Independent processing unit within a CPU.
Cache — Fast memory on the CPU storing frequent instructions/data.
Embedded System — Computer system built into a larger device for a specific purpose.
Control Unit (CU) — Manages FDE cycle and controls data flow.
Arithmetic Logic Unit (ALU) — Performs calculations and logic operations.
Accumulator — Register storing results of computations.
Von Neumann Architecture — System where CPU and memory interact via registers and the FDE cycle.