CODEWITHSUNDEEP
bootbootloader
Billy
Billy

Reputation: 1293

How does a computer know where in the filesystem the bootloader is located?

How does a computer know where in the filesystem the bootloader is located? Is there a common file among all operating systems and all computers (maybe not all computers, but all architectures) that points to the bootloader? I know Raspberry Pi always loads bootcode.bin from the first partition of the SD card. Do PCs share a common file like this?

Upvotes: 6

Views: 839

Answers (2)

alan7678
alan7678

Reputation: 2311

It is different among different architectures. But usually there is a register the cpu reads its first instruction from after reset to begin execution. This register is often contains the bits for an assembly jump operation to another memory address which is the address of the boot code. On the next clock cycle it will fetch the operation at that address and so on.

The hardware designer will have to determine how this is implemented. For example the first instruction could be to read from a memory address on an eeprom chip that contains the boot code.

As far as PC's go the motherboard has its own boot process which will load the OS bootloader. Hence the reason you can still startup a pc and see the BIOS without an OS installed

Or at least thats what I remember from my Comp. Arch. class forever ago.

Upvotes: 3

Tom Nijs
Tom Nijs

Reputation: 3950

The Master Boot Record occupies the first 512 bytes of the first hard disk, and is the first thing loaded by the BIOS to hand over control to a program capable of booting the desired operating system. In general, a bootloader gets installed in the MBR, removing its previous content. It is (in dual boot cases) possible for them to live in co-existence, which is known as multi-booting.

Upvotes: 5

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