A bootloader is very important for operating systems. Yet, it is often overlooked as a key component of computers. This is because it plays its role in the background, helping to activate the correct operating system. Most of the processor boards in our devices have programs pre-loaded on them. These programs are known as bootloaders.
This article explains what a bootloader is and how it works. If you’re interested in learning about what a bootloader is and how it works, this article is for you.
What is a Bootloader
When turned on, a computer has a clear state. This means that there are no programs in its memory and that its components cannot be accessed.
A bootloader helps to load the operating system or runtime environment to add programs to memory and provide access for components. It is needed to run the startup process, initialize the hardware, and pass control to the kernel, which initializes the operating system.
BIOS
The key components of a bootloader include the basic input/output system (BIOS), firmware found in the Read-Only Memory (ROM) of a PC. When the PC is turned on, the BIOS runs before any other program runs.
The BIOS is composed of the following:
- POST (Power On Self Test)
- Boot Sector Loader
- BIOS interrupts
- Setup Menu
The Setup Menu helps to adjust the parameters of the bootloader. Modern BIOS versions are used to set different parameters. This includes the boot order, which determines the devices the BIOS checks before booting.
The boot sector loader loads the first 512-byte sector from the boot disk into RAM. It is needed for the first available memory block or sector in the medium to be reserved for the record.
BIOS interrupts are device drivers relied on by bootloaders to access the screen, keyboard, and disks. Not all operating systems use BIOS interrupts.
In addition to the BIOS, there are extension ROMs. The main BIOS may start the extension ROMs.
The bootloader is usually composed of three programs:
- A boot sector program directly loaded by the BIOS at boot time
- A second stage program loaded by the boot sector program to complete the booting process
- A bootloader installer to install the bootloader and the second stage program in the boot disk.
UEFI BIOS
The evolving requirements of computer users have led to the creation of a modern successor to BIOS.
UEFI (Unified Extensible Firmware Interface) is a mini operating system that loads the bootloader in the memory before it executes additional operational routines.
While it shares some similarities with BIOS, several key differences have led many to consider UEFI as an extension rather than a replacement traditional BIOS.
One of the main differences between UEFI and BIOS is how UEFI provides an operational interface for computers and uses new mechanisms and functions. Additionally, while UEFI does not define how firmware should be programmed in its entirety, it does influence the interface between the firmware and operating system.
The UEFI program is permanently located on a memory chip on the motherboard. This means it is retained even when there is no power. A unique operational layer is used to communicate between the firmware and the operating system. UEFI mode can be initialized before the operating system is started up.
Some of the key advantages of UEFI include:
- It does not require an active operative system for network functionality
- Better usability through the use of a computer mouse and a graphical user interface
- Improved security through the Secure Boot feature
- A flexible modular structure that helps it adapt to special hardware environments and requirement profiles
- Boot manager, which manages different bootloaders for various operating systems
- A command-line tool for carrying out diagnostics and troubleshooting
The purpose of Secure Boot is to improve security. Parts of the UEFI firmware, the bootloader, and the operating system kernel must be verified before starting up. The components are verified using cryptographic digital signatures in the signature database of the UEFI firmware. The system boot may be canceled if the security check is not passed.
In professional environments, Secure Boot is typically used with a hardware component. The Trusted Platform Module (TPM) is a key component of Secure Boot, providing security features for computers.
When compared against the traditional legacy BIOS system boot method, the following advantages can be gained from UEFI and GPT offers the following advantages:
- Allows for multiple operating systems with their own boot managers to be installed at the same time.
- Boots faster than legacy BIOS systems
- Supports pre-boot applications
These days, an NVRAM (non-volatile random access memory) is used for boot-related settings. The settings are stored after the computer is turned off. A small amount of power from the motherboard battery is used.
How Does a Bootloader Work?
After a computer is turned on, information about the installed hardware comes up on the screen. The bootloader places its operating system into the memory. The basic input/output system (BIOS) carries out tests before transferring control to the Master Boot Record (MBR), which contains the boot loader.
A lot of bootloaders are configured to give users different booting options. The options include different operating systems, different versions of the same operating system, operating system loading options, and programs that run without an operating system.
In certain cases, a device may have two operating systems. Bootloaders can be used on these devices to start the correct operating system that users prefer automatically. A bootloader can also be used to boot the operating system into safe mode for recovery.
You can use a bootloader to boot into a program without having to start the operating system. This can be useful with devices such as game consoles. After the game disc is inserted into the console and the console is turned on, the user is taken straight to the game instead of the welcome screen.
Exceptions and Interrupts
Bootloaders are very important for the maintenance of security and software architecture. Exceptions and interrupts may be handled differently by bootloaders and applications. The method by which the hardware and software are linked directly affects how the exceptions and interrupts operate and affect the functionality of the bootloader.
About The Author
