I understand that the BIOS is in ROM, and the manufacturer "typically" designs it to point to the first sector of the "active" storage device's first sector or CHS (0,0,1)*physical and CHS (0,0,0)*logical which is either an MBR or VBR based on your preference of partitioning.
The presence of an IBM PC compatible boot loader for x86-CPUs in the boot sector is by convention indicated by a two-byte hexadecimal sequence 0x55 0xAA (called the boot sector signature) at the end of the boot sector (offsets 0x1FE and 0x1FF). This signature indicates the presence of at least a dummy boot loader which is safe to be executed, even if it may not be able to actually load an operating system.
The boot signature identifies the boot loader using a two-byte hexadecimal sequence, so I'm guessing the signature has to be an offset in the same sector? Therefore then assuming the boot loader must be in this same sector?