Boot sequence of a PC

Introduction

When one starts a PC, the BIOS tries to load a boot program in memory at address 0000h:7C00h. Then control will be given to the first byte of this region. It thus has to be an instruction.
Note: you may have heard that the first instruction executed by the processor is located at address FFFFFFF0h. This is true for Intel processors (at least some of them) but this concerns hardware manufacturers. At this location in memory they put the code that will do what is described in this page (loading the boot sector in memory and giving control to the first byte).

From a disk

If the PC is started with a system disk, it is the first physical sector of this disk that will be loaded at address 0000h:7C00h, it is called the boot sector (head 0, track 0, sector 1).

After the BIOS has loaded the boot sector into memory, the computer will execute the instruction at 0000h:7C00h and those that follow.

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