glocks1123

The BIOS starts goes through the post and hardware configuration and what not and then attempts to find a boot device. Depending on the boot priority if there is no floppy or CD the BIOS will look at cylinder 0, head 0, sector 1 of HD one. The BIOS will pass control over to the OS. Now my question is, is there suppose to be some distinct instruction at cylinder 0, head 0, sector 1 like a jump or can the OS's code just start there?

Cromewell

The BIOS looks at the boot record for instructions on where to pass the boot sequence off to (the system's boot loader).

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PC eye

Upto the first 100mb on a drive is generally used for the master boot record(mbr) along with the boot partition information. On a Windows based machine that will contain instructions for locating the boot loader like Cromewell has explained there.

On a Linux based or another OS the boot loader may not be on the actual hard drive itself but on removable media such as Grub or Lilo boot floppy. For mulitple OSs you may see the use of a universal type boot loader that needs installattion into the first part of the hard drive. A graphical user interface(gui) is then used to select the OS that will be loaded.

glocks1123

So i assume that means i can begin instructions at cylinder 0, head 0, cylinder 1 and the BIOS will treat this is if it were the boot loader?

Cromewell

I'm not entirely sure what you are trying to do but the mbr wiki should help. http://en.wikipedia.org/wiki/Master_boot_record

__________________

You know what the chain of command is? It's the chain I go get and beat you with 'til ya understand who's in ruttin' command here.

I must plug a couple comics because they are good :D:
www.ctrlaltdel-online.com
www.userfriendly.org

PC eye

The only information placed at the beginning of a drive either done by the Windows installer or the drive partitioning tool used. The information there generally is not directly accessible for the user to modify. For custom booting configurations you would still use a utility only prepared for that. That portion of any drive remains hidden from view.

glocks1123

Say i were to write my own OS and bootloader, could i place the bootloader at the beginning of the HD?

Cromewell

Yes.

__________________

You know what the chain of command is? It's the chain I go get and beat you with 'til ya understand who's in ruttin' command here.

I must plug a couple comics because they are good :D:
www.ctrlaltdel-online.com
www.userfriendly.org

tlarkin

You can download the source of boot loaders like GRUB for example and customize your own GRUB boot menu. If you look at the ultimate boot disk, I think its a complete GRUB menu for all the utilities.

PC eye

Ubuntu had a boot manager on floppy that if you can get it installed onto the front end of the drive will detect and load "any" OS whether Windows, Linux, Mac, etc. at one point. When booted from floppy it just about guaranteed to load any OS by clearly indicating any and all partitions with the choice to whatever one was on the one you selected. I lost the site before going into it further to see if a cd or install to drive option was found. That would solve any custom boot situations you wanted.