Previously Ann Onimus said:
Hello
will somebody please explain to me in plain words what is MBR, partition
table, NTDLR and boot sector?
Yes, I have googled this but some plain words will do just nicely...
Any storage medium is a succession of sectors, numberd e.g. from 1 to n.
Sector size is traditionally 512 Bytes but can be 1kB or 2kB
(CDROM, some MODs).
If you have an unpartitioned medium (traditionally the floppy),
then the boot sector is the first sector. It containes the
boot loader code (the programm that is started when booting from
this medium) and geometry infromation for the medium.
If you have a partitioned medium, e.g. a harddrive, things are more
complicated. The first sector now is a partition table sector, that
also serves as the MBR. It does specify the size and place of the
first four partitions, the primary ones. If one of the partitions is
an extended partition (a type of primary partition) then it has its
own partition table, typically specifying the first logical partition
and the place of a (potential) next partition table sector that
specifies the next logical partition and so on. So the partition table
is really 4 primary entries in the MBR and a potential chain of more
partition table sectors pointed to by one of the entries.
Just as the boot sector, the MBR contains a small programm that is
executed by the system BIOS on booting from that medium.
Now the NT-loader is part of the windows world. I don't know
too much about it, my explanation may be wrong here.
If the boot code in the MBR is from Microsoft, then it will be pretty
stupid (alternatives e.g. Grub). It will look for a primary partition
that is "active" (has a flag set) and execute the boot-sector of
it. The boot sector of a partition is its first sector.
This boot-sector will load the NT-loader software from the
disk. AFAIK its position (sector number(s)) is hard-coded in the
boot-sector, so moving the file will make the partition unbootable.
(Not sure about this.) The boot-sector will then load and
execute the NT loader and this software will load the OS.
Grub will also execute from the MBR, but form then onwards it will
load it shell, look for its configuration file in the filesystem and
present you with a menu and (if you want more selection) with a shell
that even allows you to browse partitions and files to some
degree. Once you made your selection it will either load and execute
the boot-sector of a partition (in order to boot Windows from it) or
load and execute a kernel file directly (for Linux and other OSes that
do not insist to start themselves).
For more detail, resort to google again.
Arno
