In order to be able to execute commands and applications, the processor of a PC always uses the RAM memory, because this is where the information and calculations that the processor must constantly use to perform its tasks are stored.
Obviously, the most important resource stored in RAM concerns the operating system, a “program” with a process management function that regulates, among other things, CPU access to memory with precision (and although it seems redundant). What we mean by this is that on a PC the relevant operating system data must be loaded into memory as soon as the computer starts up, and this is where the bootloader kicks in.
What is a bootloader?
As you can imagine, because its name is pretty self-explanatory, the word bootloader comes from the English words boot (boot) and loader (loader), although to be more precise it actually comes from boot loader, which in English literally means charger (or buckle) of the laces of the boots. The origin of this term comes from the fact that the boot manager is essential when starting the PC and, therefore, serves as a support in a similar way to what lace loops do.
A bootloader is a kind of special software that loads essential operating system files that you have in your computer’s RAM memory, and this goes for Windows, Linux, Max and even DOS-based systems like FreeDOS. To do this, the bootloader must be used on a bootable system, which could very well be a CD / DVD, a USB stick or the system storage unit, which is common on a PC.
The bootable media receives the information about the location of the bootloader through the firmware of the computer, such as the BIOS, for example, and this is precisely the reason why in the BIOS we can configure the devices of start-up.
By selecting the boot sequence in the BIOS, we literally tell the PC where to look for the bootloader, because without it the computer cannot start and boot the operating system.
How a PC bootloader works
The moment we press the power button on the PC, the first thing that appears on the screen is the data relating to the hardware of the equipment, such as the processor, memory or connected storage devices. The software responsible for processing this information is the aforementioned firmware (BIOS / UEFI on a PC) present in the ROM memory of the motherboard.
This initial process is called POST, which means Power-on self-test And although we have a specific article on this, in short, it consists of a series of processes and system checks that are performed on the PC every time it is turned on or restarted. And, as you will already assume, the bootloader is what is loaded right after POST; The system checks the boot sequence configured in BIOS and begins to scan so that the first of the selected devices that has a boot loader load the data into memory.
When a media with boot loader is found, it will load automatically, but if the list of configured devices in BIOS ends and none are found, the system will display an error message and will not boot. . The bootloader is, as you will assume after reading this, essential and essential for the functioning of the computer.
Where exactly is it stored?
The bootloader is usually located in the MBR (Master Boot Record) of the hard drive or SSD, where the partition table of the storage media is also stored, however this is not always the case and as a rule these two can be found. options:
- In the first block of the bootable media (also called “zero disk track”).
- On a specific partition of the bootable media.
The first option is the most common because it is closely related to the working principle of the MBR, which not only contains the necessary reference to the firmware to find the bootloader but also contains the boot software itself, which the system allows. operation to start. “
In the second option, which is less used because it requires the user to have it configured this way on purpose for some reason (although it also looks like this on OEM PCs from manufacturers), the operating system uses a partition specific as the storage location for the bootloader that is created on the storage drive.
As additional information, be aware that bootloaders can also be split into multiple levels in a configuration called multi-storey and that it can cover up to three different levels, running one after the other. This is used when the boot loader is too large to fit on the zero track of the disk.
His homeworks ?
After what has been explained so far, you will have already understood that boot loaders are a kind of intermediary between the hardware and the operating system of the PC. You could say that the responsibility for starting the system lies with this element, and for this its first task is to load the operating system into the computer’s RAM, which is essential for the processor to know what to do.
In the next step, the boot loader loads the operating system kernel, the fundamental component of system software that controls all access to memory and processor and contains all essential drivers. In addition, it handles all routine commands and tasks such as data memory integration. Some boot loaders perform additional tasks that go beyond simple boot loaders, such as:
- Recognition and start of other boot loaders (multi-stage).
- Execution of application programs.
- Correct or add incorrect functionality in the firmware.
- Alternative firmware download.
What are boot loaders?
So far we have explained to you what a bootloader is, what are its functions and what it is for, but you should also know that there are different bootloaders depending on the use and the operating system. We have summarized the most important in the following table:
|last name||The description|
|last nameBootmgr||The descriptionThis is the Microsoft bootloader from Vista / Server 2008|
|last nameNT-Loader (NTLDR)||The descriptionThis is the bootloader that Microsoft used until the arrival of Vista (i.e. until Windows XP / Server 2003)|
|last namebare box||The descriptionIt is a bootloader built into scanners, printers, cameras, etc.|
|last nameboot.efi||The descriptionIt is the bootloader used by Mac devices since 2006.|
|last nameBootX||The descriptionOld bootloader used by Macs until 2006.|
|last nameGRUB (Large Unified Bootloader)||The descriptionIt is an open source bootloader known to be the one generally used by Linux systems.|
|last nameARM Core Bootloader||The descriptionBootloader used in microcontrollers (as in smartphones)|
|last nameOpenBIOS||The descriptionIt is a free and portable bootloader under the GNU-GPL license.|