Strange booting problem

[Gordon Messmer]

On 06/30/2015 03:17 PM, jd1008 wrote:
> The link you refer to
> talks about the 2 bytes past byte 255, they they are
> bytes 256 and 257.

No, they're the two byte block at the 255th block of two bytes.

https://en.wikipedia.org/wiki/Master_boot_record

Again, bytes 0-446 are boot code.  Bytes 256 and 257 are not special 
locations, they fall within the boot sector.  Bytes 511 and 512 (or, 
bytes at offset 510 and 511) are the boot signature.  When present, that 
signature indicates that a boot sector is present and can be used.  
Testing indicates that if the signature is present, BIOS will load that 
sector into memory and continue execution of the code that it contains.  
Control will not return to BIOS.

> But I already indicated the 466 bytes are null...

Doesn't matter.  The documentation doesn't say that the contents of the 
446 bytes are tested.  nul bytes are valid opcodes in x86.

> So, the laptop's BIOS is executing what?

Whatever it finds in the first disk that has a valid boot signature.  
Once it finds a disk with a signature, it passes execution to the boot 
sector and does not continue searching.