HUMOR: Soutez : Bootovani

[Zdenek Kabelac]

Miroslav BENES wrote:
 > > PC BIOS neumi bootovat z niceho jineho nez z prvnich 4 partition a
> > MBR.
> A co disketa, CDROM, NET ... :-))
> Krome toho jedna z tech 4 partition  muze byt typu extended - a pak
> je toto tvrzeni scestne. Navic spojeni "prvnich 4" je taky
> zavadejici, protoze vic nez 4 byt standardne nemuzou :-)

Bavime se o bootovani z IDE hdd a ne o floppy, zip, a:drive, CDROM, SCSII
a vsem o statnim :-)

> Navic PC BIOS se o partisny VUBEC NESTARA !

Ale stara a jak - pokud mas spatny bios a velky disk, tak se ti vyrazne
komplikuje zivot - a navic pokud je v biosu brutalni bug tak se pak
takovy pocitac neda s DOSem ani pouzivat a ja vim o cem mluvim,
nebot jsem takovy BIOS v pocitaci mel.

> Pri zavadeni systemu z HDD (u novejsich BIOSu z kterehokoliv) se
> nacte MBR do pameti a preda se mu rizeni. Existuji non-DOS zavadece,

HLUBOKY omyl - doporucuji si precist jakokoliv dokumentaci nejlepe od
bootloaderu GRUB
Pro jisototu priklad velmi kratky vytah:

  Bootloader Size Limits

   Bootloaders have to be very small, typically limited to one or more
   very small areas on the media in question.

   At the start of the process, the BIOS loads the first block off of the
   boot disk (floppy or hard drive), 512 bytes in size. This one block
   must be capable of performing all the functions necessary to start up
   the system, or handing off to another program. On a hard disk, at
   least 64 bytes are reserved for a partition table, therefore unusable.

   Traditionally, if the first block is not enough, at the start of the
   partition with the OS being booted (or, for a floppy, just at the
   beginning) is a fixed area, the size (generally from 512 bytes to 8
   Kbytes) of which is dependent on the filesystem variety in question.

   Most bootloaders are written to fit within this limitation, giving
   them only room for a very sparse functionality.

.... skip ....

   The traditional layout of a hard disk on a PC is with the first block
   being the boot-controller, referred to as the MBR (Master Boot
   Record), with the rest of the disk subdivided into 4 sections (called
   "partitions"), each of which look either like a logical floppy (boot
   block + filsystem), or a full hard disk (sort of a recursive
   definition here, though only one of the partitions can be one of
   these). Inside one of the recursive hard disk definitions, only one of
   the 4 partitions can have a filesystem. The pratical result is that an
   arbitrary number of partitions can be represented. The biggest problem
   here is that generally only one of the 4 partitions listed directly in
   the main MBR can be the "active" one, which is the one where any
   subsidary boot blocks are pulled from.

   Most bootloaders don't deal with the "active partition" marker in a
   very intelligent manner.


atd.. - velmi podrobne popsano do posledni bitovych detailu.
Doporucuji precist - tim se vyhnete jakekoliv mystifikaci siroke verejnesti
:-)

> ktere se takto aktivuji a vyuzivaji (udajne) dalsi sektory z pvrni
> stopy, ktera je jinak nevyuzita - pokud pomineme viry a podobnou
> havet. Takovy program se tedy zavede bez vyuziti jakekoliv partisny
> a on sam pak muze udelat prakticky cokoliv - treba predat rizeni na
> logicky disk z extended (kde neni definovan MBR, ale boot-sektory
> ano).

Ale samozrejme ze se zavede podle definovanych partition.
Viz vyse - opravdu je to dobre cteni....


-- 
     Linux is like a wigwam - no windows, no gates, apache inside!
   Zdenek Kabelac    http://www.fi.muni.cz/~kabi/   kabi na fi.muni.cz