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Overview
This note covers the boot process and file systems for Windows and Linux. It includes hardware initialization via BIOS/UEFI, disk partitioning schemes, file system types, and the full boot sequence from POST through kernel initialization to user login.
Terminology
| Term | Definition |
|---|
| BIOS | Basic Input/Output System; legacy firmware interface managing the boot process |
| UEFI | Unified Extensible Firmware Interface; modern BIOS replacement with larger drive support and Secure Boot |
| POST | Power On Self Test; hardware initialization and error check before booting |
| MBR | Master Boot Record; 512-byte boot sector containing boot loader and partition table |
| GPT | GUID Partition Table; modern MBR replacement supporting larger disks and integrity checks |
| GRUB | Grand Unified Bootloader; common Linux boot loader |
| Partition | Logical division of a physical disk into separate storage segments |
| Sector | Smallest addressable unit on a disk; typically 512 bytes |
| Metadata | Data about data — e.g., MFT in NTFS, FAT tables |
| Allocated Space | Disk blocks actively used by files |
| Unallocated Space | Free disk space not assigned to any file |
Core Concepts
Hard Drive Types
| Drive Type | Description |
|---|
| HDD (Hard Disk Drive) | Magnetic platters divided into sectors; slower, mechanical |
| SSD (Solid State Drive) | Flash memory in NAND cells; no moving parts; faster and non-volatile |
Commands: fdisk -l — view disk info | parted -l — view unallocated space
Firmware — BIOS vs UEFI
| Feature | BIOS | UEFI |
|---|
| Age | Legacy | Modern |
| Drive Size Support | Limited | Large drives (2TB+) |
| Boot Speed | Slower | Faster |
| Security | Basic | Secure Boot support |
| Partition Style | MBR | GPT |
Partitioning — MBR vs GPT
| Feature | MBR | GPT |
|---|
| Max Drive Size | 2TB | 9.4ZB |
| Max Partitions | 4 primary | 128 |
| Integrity Checks | No | CRC values stored |
| Associated Firmware | BIOS | UEFI |
MBR structure: Boot Loader (446 bytes) | Disk Partition Table (64 bytes) | Magic Number AA55 (2 bytes)
File Systems
Windows
| File System | Use Case |
|---|
| FAT | Legacy systems |
| NTFS | Modern Windows — see Windows Fundamentals for permissions detail |
Command: fsutil fsinfo ntfsinfo C: — view NTFS file system info
Linux
| File System | Use Case |
|---|
| ext3 | Older Linux systems |
| ext4 | Standard modern Linux file system |
Commands: mount | column -t — view mounted file systems | df -h — view disk space allocation
macOS / iOS
- APFS (Apple File System) — default on modern Apple devices
Boot Process — Linux
- BIOS/UEFI — runs POST, executes MBR
- MBR — loads GRUB
- GRUB — executes the Linux kernel
- Kernel — loads
/sbin/init
- Init — executes runlevel programs from
/etc/rc.d/rc*.d/
| Init System | Description |
|---|
| SysV | Traditional boot system using runlevels |
| Systemd | Modern init system; flexible and robust |
Systemd unit types: .service | .mount | .target
Commands: systemctl list-units — list active units
Boot Process — Windows
- BIOS/UEFI — runs POST, executes MBR
- MBR — executes Windows Boot Manager (WBM)
- Windows Boot Manager — loads Windows OS Loader
- Windows OS Loader — loads NT OS Kernel
- NT OS Kernel — executes
smss.exe and csrss.exe
- Winlogon —
wininit.exe reaches login screen
- Explorer —
explorer.exe runs after user login
References / Images
- BIOS vs UEFI comparison diagrams
- MBR structure diagram
- Linux SysV vs Systemd boot flow diagrams
- Windows boot process illustration
