Can a (second) hard disc consist of only 1 extended/logica..

In comp.os.linux.hardware VanguardLH <V RemoveThis @nguard.lh> wrote:

| After the BIOS completes its POST (power-on self test), it loads the
| bootstrap program from the MBR (master boot record) from the first hard
| disk that it finds. The first sector of the hard disk is the MBR and is
| not allocated to any partition (as well as the remaining 62 sectors of
| the first track on the hard since tracks are assigned in 63-sector
| increments). The first 446 bytes are the bootstrap program. So the
| BIOS needs to load the bootstrap program into memory and pass control to
| it. The BIOS *only* looks for the bootstrap program from the MBR on the
| *first* hard disk detected.

That should be "WHEN tracks are assigned in 63-sector increments".
Although all hard drives today do use that number as the default, at one
time that was not true. You can still label/format the drive to specify a
different value, as well. I've done this specifying 8-sector increments
and it works fine in Linux (have not tested other systems). I regularly
do that on my USB flash keys. I'd do it on my SD(HC) memory cards if my
camera would accept it. But for some reason it gets confused, so I leave
it in the form originally on the memory card when I got it (I saved a
compressed copy of the original content image of the memory card so I
can restore it, as a means to reset the card).


| This is the old BIOS scheme of how to boot a system. The BIOS loads the
| bootstrap program in the MBR from the first detected hard disk which
| reads the partition tables in the same MBR to then load the OS boot
| loader in the primary partition marked as active and which can only
| reside on the same hard disk since partition tables only delineate areas
| on that hard disk. Other software-based schemes have evolved that
| replace the OS boot loader in the first sector of the partition (that
| the MBR bootstrap loaded), the OS loader lets you specify from where to
| load the actual OS (like Microsoft's dual-boot), or they replace the MBR
| bootstrap program to eliminate the restriction that the boot partition
| is primary or even has to be on the same hard disk. So with a multiboot
| manager replacement for the bootstrap program, you can boot to any type
| of partition (primary or to a logical drive under an extended partition)
| which can be on any hard disk. Some BIOSes have been extended to
| perform the same functionality as the software multiboot managers to
| allow booting from any partition or logical drive on any hard disk.

And some even allow booting from a specific sector offset from the whole
disk, allowing placement of the kernel image (or stage 2 image of a boot
loader) in the space intentionally left between partitions. You better
know what you are doing if you want to do stuff like that; it's not for
newbies in a production environment.

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| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
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