COLD BOOT
From power button to shell prompt
A 25-article series explaining how a computer actually starts. Every step, from voltage on a wire to your first shell script. No prerequisites assumed.
Start ReadingThe Series
Hardware
Voltage, signals, buses, and memory -- the physical foundation everything else sits on.
Firmware
BIOS, UEFI, POST -- the first code that runs before any operating system loads.
Boot
Bootloaders, GRUB, kernel loading -- bridging firmware to the operating system.
Kernel & OS
Init, processes, filesystems, drivers -- the operating system takes control.
Shell
TTY, I/O, pipes, environment -- from login prompt to your first script.
Articles
Your First Shell Script
A shell script is a text file that the shell reads as a sequence of commands.
ShellThe Environment
Environment variables are how the shell and programs share configuration.
ShellPipes and Redirection
The power of Unix comes from connecting programs together with pipes.
ShellStandard I/O
Every process has three channels: standard input, standard output, and standard error.
ShellWhat a Shell Actually Is
The shell is not the terminal. It is a program that reads commands and runs them.
ShellUsers, Groups, and Permissions
Linux controls access through a simple system of users, groups, and permission bits.
SecurityThe TTY and Terminal
The terminal you type into has a history that goes back to mechanical teletypes.
OSThe Process Model
Every running program is a process. The kernel manages them all.
OSPID 1: init and systemd
The first userspace process starts everything else. It is process number one.
OSThe Root Filesystem
Before the system can do anything useful, it needs to mount its root filesystem.
OSDevice Drivers
The kernel cannot talk to hardware directly. Drivers are the translators.
KernelThe Clock Signal
Every operation in a computer happens in time with a clock. This is how timing works.
HardwareKernel Init
The kernel takes control of the hardware and begins building the operating system.
KernelDecompressing and Handing Off
The kernel image is compressed. Before it can run, it must unpack itself.
BootFinding the Kernel
GRUB locates the kernel image on disk and prepares to load it into memory.
BootStage 2: GRUB
GRUB takes over from the bootloader and gives you a menu. Here is what it does next.
BootStage 1: The Bootloader
The first tiny program that loads from disk. It has one job: load something bigger.
BootFinding the Boot Device
The firmware searches for something it can boot from. This is how it decides.
BootThe Bus System
How the CPU talks to every other component through shared communication channels.
HardwareMemory Initialization
RAM does not work until the firmware trains it. Here is what that means.
HardwareUEFI vs Legacy BIOS
Two generations of firmware and why the transition matters.
FirmwareWhy Linux?
Why this series uses Linux as its reference operating system.
LinuxPOST and the BIOS
The first software that runs is not your operating system. It is the firmware.
FirmwareThe Reset Vector
The CPU wakes up at a hardcoded address. Everything starts from that one location.
HardwareThe Moment Power Arrives
What happens in the first nanoseconds after you press the power button.
HardwareBits, Bytes, and Voltage
Every computation starts with a physical signal. This is how voltage becomes meaning.
Foundations