$WW,1$When you turn-on (better term is "power-up"!) a computer or do a hardware reset, it starts in the $FG,2$BIOS$FG$.  Sometimes, you must change the $FG,2$BIOS$FG$ boot order to boot stuff.

The $FG,2$BIOS$FG$ loads a boot sector from CD-ROM or hard disk or floppy or whatever.  The boot sector runs in 16-bit 80x86 mode and often loads-in a second file that's bigger if it can't be done by just one sector.  It's a safe bet that boot sectors are hand-coded assembly language  Most boot sectors use the $FG,2$BIOS$FG$ to load-in the rest, but I gave-up trying to get that to work and my boot sectors do direct access to hard-drive or CD-ROM to load-in subsequent modules.

Not only do boot sectors have a size limit, 512 bytes or 2048 bytes, the files they load have to fit within 640K because they run in 16-bit mode.  This means they usually can't just load the whole operating system and start it running.  The operating system must load the rest of itself.  My $FG,2$OSMain$FG$ module is what the boot sectors load and I try to put a minimum in it so it will always fit in 640K.  It switches to 32-bit mode, then 64-bit allowing access to more memory, and loads in the rest.

All the boot related stuff for LoseThos is in the $FG,2$/LT/Utils/Boot$FG$ directory.

$LK,"BootCD.SPZ","FI:::/LT/Utils/Boot/BootCD.SPZ"$
$LK,"BootFD.SPZ","FI:::/LT/Utils/Boot/BootFD.SPZ"$
$LK,"BootMHD.SPZ","FI:::/LT/Utils/Boot/BootMHD.SPZ"$
$LK,"BootMHD2.SPZ","FI:::/LT/Utils/Boot/BootMHD2.SPZ"$
$LK,"BootHD.SPZ","FI:::/LT/Utils/Boot/BootHD.SPZ"$

$FG,2$BootCD$FG$ is the CD-ROM boot sector.  If you are curious on the layout of $FG,2$ISO9660$FG$ CD-ROMs, see $LK,"DiskCDDVD.APZ","FI:::/LT/Adam/DiskCDDVD.APZ"$.  To make a custom bootable CD-ROM, look here $LK,"Bootable CD","FF:::/LT/Doc/FileManager.MUZ,BurnProdu"$.

$FG,2$BootMHD$FG$ is the master boot record for a hard drive.  This goes on block zero.  It loads-in $FG,2$BootMHD2$FG$.  It displays a menu and will boot to a partition.  Each partition has it's own partition boot record.  $FG,2$BootHD$FG$ is the boot record for a LoseThos partition.

Boot record code doesn't usually access directories because that would make them too big and would make them depend on a file system layout.  They need raw block addresses to load other stuff.  To update with a new LoseThos kernel ($FG,2$OSMain$FG$), you must create a binary file and modify the boot loader so it knows the blocks to load.  Therefore, you usually recompile the kernel and update the boot sector at the same time.  $LK,"InstallBoot","MN:InstallBoot"$() does this.

With LoseThos , the $FG,2$OSMain$FG$ module loads the compiler module so it can process start-up scripts and work with source code from then, on.  $LK,"::/LT/OSMain/AdamK.APZ","FI:::/LT/OSMain/AdamK.APZ"$ is the starting start-up script.  It processes (compiles into memory) the stuff in the $FG,2$/LT/Adam$FG$ directory and ends by $FG,2$#include$FG$ing the $LK,"HOME/Adam3.APZ","FI:HOME/Adam3.APZ"$ file.

It is possible to reboot without doing a hardware reset.  This is faster when working on $FG,2$OSMain$FG$ or your start-up scripts.  See $LK,"BootLT","MN:BootLT"$().

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