Re: How does linux boot

[Martin Dickopp <martin-deb@zero-based.org>]

Ritesh Raj Sarraf <riteshsarraf@users.sourceforge.net>(by way of Ritesh Raj Sarraf <riteshsarraf@users.sourceforge.net>) writes:

> So, Is the boot-loader so smart and powerful (much more that the
> kernel) that it reads data from the disk without knowing the type of
> disk and the filesystem type ? I mean the kernel requires modules to
> be loaded to detect the type of disk (scsi or ide) , type of
> filesystem etc.. The boot-loader doesn't require anything ? Amazing.

The BIOS knows how to access the disk physically (i.e. how to load a
certain sector given its sector number). If your mainboard has a SCSI
interface, its BIOS knows how to access disks connected to it. If you
have a separate SCSI card, it (i.e. the card) contains some BIOS code to
access the disks connected to it.

However, BIOSes usually access disks in a very simple, backward
compatible, slow way. While many OSes did indeed use the facilities of
the BIOS for all disk access until the late 1980's or early 1990's, this
would be *much* too slow for anything but initially loading the kernel
on more modern systems.

Some bootloaders (e.g. grub) do indeed have the capability to interpret
filesystems. Others just record the information in which sectors the
kernel is stored, so they don't have to interpret the filesystem in
order to load the kernel.

Martin


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