This article is another case of regurgitated received folk wisdom that is wrong and that has been wrong for years if not decades.
> The processor starts working in real mode.
Intel CPUs have not started in real mode since the 80286. The 80386 and later start in unreal mode. The whole explanation of real mode addressing, based upon not realizing that the 80386 and later always use the segment registers and do not do that real mode address calculation using the value of the selector, is irrelevant. Futhermore: In some scenarios nowadays, CPUs never run in real mode, going straight from unreal mode to protected mode and, because they then run a protected mode EFI bootstrap, staying there.
> When attempting to boot from a hard drive, the BIOS tries to find a boot sector.
PC systems have not necessarily loaded the MBR and run it for more than a decade, now. Systems bootstrap the EFI way, and this is nowadays fairly common and mainstream.
> The core image begins with diskboot.img, which is usually stored immediately after the first sector in the unused space before the first partition.
This "boot virus area" does not exist on modern systems with EFI partitioning. That is also common and mainstream nowadays, too.
Quoting directly from the manual
"Intel® 64 and IA-32 Architectures
Software Developer’s Manual
Volume 3"
"
9.1.4 First Instruction Executed
The first instruction that is fetched and executed following a hardware reset is located at physical address
FFFFFFF0H. This address is 16 bytes below the processor’s uppermost physical address. The EPROM containing the
software-initialization code must be located at this address.
The address FFFFFFF0H is beyond the 1-MByte addressable range of the processor while in real-address mode. The
processor is initialized to this starting address as follows. The CS register has two parts: the visible segment
selector part and the hidden base address part. In real-address mode, the base address is normally formed by
shifting the 16-bit segment selector value 4 bits to the left to produce a 20-bit base address. However, during a
hardware reset, the segment selector in the CS register is loaded with F000H and the base address is loaded with
FFFF0000H. The starting address is thus formed by adding the base address to the value in the EIP register (that
is, FFFF0000 + FFF0H = FFFFFFF0H).
The first time the CS register is loaded with a new value after a hardware reset, the processor will follow the normal
rule for address translation in real-address mode (that is, [CS base address = CS segment selector * 16]). To
insure that the base address in the CS register remains unchanged until the EPROM based software-initialization
code is completed, the code must not contain a far jump or far call or allow an interrupt to occur (which would
cause the CS selector value to be changed).
"
> The processor starts working in real mode.
Intel CPUs have not started in real mode since the 80286. The 80386 and later start in unreal mode. The whole explanation of real mode addressing, based upon not realizing that the 80386 and later always use the segment registers and do not do that real mode address calculation using the value of the selector, is irrelevant. Futhermore: In some scenarios nowadays, CPUs never run in real mode, going straight from unreal mode to protected mode and, because they then run a protected mode EFI bootstrap, staying there.
> When attempting to boot from a hard drive, the BIOS tries to find a boot sector.
PC systems have not necessarily loaded the MBR and run it for more than a decade, now. Systems bootstrap the EFI way, and this is nowadays fairly common and mainstream.
> The core image begins with diskboot.img, which is usually stored immediately after the first sector in the unused space before the first partition.
This "boot virus area" does not exist on modern systems with EFI partitioning. That is also common and mainstream nowadays, too.
* https://superuser.com/a/347115/38062
* https://superuser.com/a/345333/38062
* http://jdebp.eu./FGA/efi-boot-process.html
* http://rodsbooks.com./efi-bootloaders/index.html