Question

If you have a PC, record the sequence activities that you can observe when you turn it on. Then determine what messages appear on the computer screen before the booting process actually begins. What software writes these messages?

Short answer

The BIOS/UEFI writes messages before the booting process begins.

Step-by-step solution

Observing the Boot Process

When you press the power button on the PC, the boot sequence begins. The first observable activities are usually the fans spinning up, followed by lights turning on, and in some cases, a beep sound from the PC.

Understanding BIOS/UEFI Phase

Shortly after the physical activities, observe the initial text messages appearing on the screen. These messages are typically displayed by the BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) firmware. They perform a Power-On Self-Test (POST) to ensure all hardware components are functioning correctly.

Identifying Pre-Boot Message Source

The messages that appear before the operating system loads are written by the BIOS or UEFI. They include manufacturer information, device configuration details, and memory checks.

Transitioning to Boot Loader Phase

After the initial messages, control is transferred from the BIOS/UEFI to the bootloader, such as GRUB or Windows Boot Manager. This marks the actual start of the operating system booting process.

Key concepts

BIOS

The Basic Input/Output System (BIOS) is the firmware that starts when you power on your PC. It's the software embedded on a small memory chip on the motherboard. The primary job of the BIOS is to boot the system and manage the data flow between the computer's OS and attached devices like the hard drive, video adapters, keyboard, mouse, and printer.

BIOS initializes and tests the system’s hardware components and loads a bootloader or an operating system from a mass memory device. Before the boot process begins, BIOS checks to ensure that all necessary components are functioning correctly. This ensures that your PC has a clean setup for the operating system to start its processes. If there's an issue, BIOS can often report errors, usually in the form of beeps or error messages displayed on the screen.

UEFI

The Unified Extensible Firmware Interface (UEFI) is the modern replacement for BIOS. UEFI is more robust and capable of handling larger drives with support for more complex features than its predecessor. It’s a crucial component of the boot process, working like BIOS but with enhancements that provide a smoother experience.

UEFI performs similar functions to BIOS but offers more advanced features, such as graphical interfaces, network capabilities, and faster boot times. It's designed to be more secure, often including secure boot which prevents the system from booting unauthorized operating systems.

• Handles drives over 2.2 terabytes
• Faster boot and resume times
• Advanced graphical interface during setup

Overall, UEFI provides a more flexible and secure framework for the boot process, increasingly standard in modern PCs.

Power-On Self-Test (POST)

POST is the diagnostic testing sequence run by a computer's BIOS or UEFI upon startup. It checks the hardware components to ensure everything is working properly before the computer goes further into the boot sequence. If the POST process identifies an error, it will usually notify the user with an error message on the display or with beeps.

If no issues are found, the POST sequence proceeds to initialize the video interface, and the details of the testing and status messages are displayed on the screen.

• Tests memory using a checksum method
• Detects and initializes devices like keyboard and disk drives
• Identifies any critical hardware faults early on

POST acts like a safety check before the computer gets into full swing. If detected issues are addressed, users can be assured of a stable operational environment.

Bootloader

The bootloader is the software that starts up your operating system after the BIOS/UEFI has verified the hardware. When the control is handed over to the bootloader, it loads the operating system into memory and passes execution control to it. The bootloader can load various OS options, particularly in dual-boot configurations.

Bootloaders such as GRUB (used in Linux systems) or Windows Boot Manager are typically very small and reside on the hard disk. Once called upon, they locate the kernel of the operating system and load it into main memory.

• Facilitates the start of the operating system
• Offers choices in multi-OS environments
• Responsible for loading essential files to memory

Without a bootloader, the operating system wouldn’t know where to start, making it a vital link in the PC boot sequence.

Operating System

The operating system (OS) is the final piece that comes into play during the PC boot sequence. It’s the interface that allows the user to interact with the computer and its hardware. Once the bootloader has loaded the OS kernel into memory, the operating system takes control.

The OS manages all other software on your PC and provides utilities that allow the user to perform tasks, run applications, and manage files.

• Acts as a bridge between hardware and applications
• Manages system resources and hardware communication
• Facilitates user input/output operations

The operating system, such as Windows, Linux, or macOS, becomes active after the bootloader has done its job, providing the necessary environment for software applications to run efficiently.