Module 0: Computer Hardware Fundamentals

Parts of PC Architecture

• CPU

• Memory

• Video Controller

• USB Controller

• Fixed Storage Controller

Bus

a communication system that transfers data between components inside a computer.

Controller

hardware device or a software program that manages or directs the flow of data between two entities

CPU

controls interpretation and execution of instructions

Parts of CPU and their functions

Registers, Arithmetic Logic Unit (ALU), Control Unit

Register

Small, fast memory inside CPU; hold instructions, addresses, or data.

ALU

Performs arithmetic and logic operations; may be split into AU and LU.

Control Unit

Directs operations of the CPU; fetches, decodes, and coordinates execution of instructions.

Fetch-Decode-Execute Cycle

Process by which CPU executes instructions continuously, millions of times per second.

Protected Instructions

Can only be executed by the operating system; prevent user programs from harming the system.

Fetch – PC (Program Counter)

Holds address of next instruction; increments after fetch.

Fetch – MAR (Memory Address Register)

Holds memory address for fetch/store operations.

Fetch – MBR (Memory Buffer Register)

Temporarily stores data/instruction from or to memory.

Decode – IR (Instruction Register)

Holds current instruction; CPU decodes it to determine operation.

Execute - (Fetch-Decode-Execute Cycle)

CPU carries out the decoded instruction (arithmetic, logic, data movement, or control flow).

Pipelining

Process of overlapping instruction execution by dividing into stages.

• Fetch

• Decode

• Execute (can occur simultaneously)

3-Stage Pipeline

Each CPU tick: one instruction fetched, another decoded, another executed.

Benefit of Pipelining

Maximizes CPU utilization; stages work independently.

Superscalar CPUs

Contain multiple fetch, decode, and execution units with buffers to handle speed differences.

Memory Hierarchy

Organized by proximity to CPU: Registers → Cache → Main Memory → Storage.

• Registers
  Inside CPU; smallest but fastest memory.

• Cache (L1, L2, L3)
  Very close to CPU; faster than RAM but smaller in size.

• SDRAM (Main Memory)
  Connected to CPU via bus; larger but slower than cache.

• Storage (SSD/HDD)
  Largest and slowest; connected to CPU via bus.

Closer to CPU = faster, smaller, more expensive.
Farther from CPU = slower, larger, cheaper.

Memory Sizes (Binary / IEC)

• 1 KiB = 2¹⁰ = 1,024 bytes

• 1 MiB = 2²⁰ = 1,048,576 bytes

• 1 GiB = 2³⁰ ≈ 1.07 billion bytes

• 1 TiB = 2⁴⁰ ≈ 1.1 trillion bytes

Booting + Why do we need it?

Process of starting a computer via hardware (button) or software command.

CPU starts with no software in main memory; a process must load software into memory before execution.

Intel i386 / x86 Overview

• Intel 386 (i386): 32-bit CPU introduced in 1985, used in workstations and high-end PCs.

• x86 Family: Based on Intel 8086/8088; ensures backward compatibility.

• Instruction Set Evolution: 8-bit → 16-bit → 32-bit.

Modern Boot Process / UEFI

UEFI: Unified Extensible Firmware Interface; standard for implementing boot processes.

Benefits: OS can access system info, manage boot disks, partitions, and configurations without entering firmware interface.

Architecture: Typically found in x64 (64-bit) systems; some x64 still use BIOS, some i386 support UEFI.

x64 vs x86: x64 = 64-bit CPU/OS, x86 = 32-bit CPU/OS.

BIOS

Basic Input/Output System; program that starts the computer after power-on. Stored in ROM.

• little standardization between BIOS

• Initialization: checks components (display, keyboard)

• POST: Power-On Self Test; beeps indicate hardware problems

Boot Device & Boot Sector

• BIOS finds boot device using NVRAM (retains info when powered off)

• Boot sector: first disk sector; contains Boot Block program → points to OS init

Boot Block & OS Loader

• Boot Block program: loads and calls OS Boot Loader

• OS Boot Loader: initializes OS; location/size vary by OS

Multiple OS / MBR

• Master Boot Record (MBR): first sector; shows OS selection menu

• BIOS loads selected partition → boot block → OS Boot Loader → OS

Modern Boot / UEFI

• UEFI: Unified Extensible Firmware Interface; replaces BIOS in most modern systems

• Standardized boot process; OS can locate system info reliably

• Allows OS to manage boot disks, partitions, and configurations without entering firmware

• Typically used in x64 (64-bit) systems; x86 = 32-bit

• Some x64 still use BIOS; some i386 support UEFI

UEFI Major Components & Roles

• EFI Manager: Controls boot sequence; locates boot device in NVRAM

• Protective MBR (PMBR): Warns older BIOS systems of UEFI disk

• Primary Header: Stores disk info (capacity, sectors, partition layout)

• Partition Entries: Metadata about partitions (labels, sizes, structure)

• EFI Partition: Contains OS bootloaders; centralizes and protects bootloaders

• Secondary Partition Entries & Primary Header Copy: Redundancy for disk integrity and recovery

ARM vs Intel / Boot

• Intel (CISC): complex instructions, one can do multiple operations

• ARM (RISC): simple, fast instructions; may need several for same task

• UEFI: standard for Intel; no standard yet for ARM, but Linux distros exploring