Contents
1.0 ) Boot sectors
1.1 ) Master boot sector
1.2 ) Dosfs boot sector
1.3 ) Minixfs boot block
1.4 ) Tar boot sector
1.5 ) Skip boot sector
1.6 ) Panic boot sector
2.1 ) Booting i86 standalone executable
2.2 ) Booting Elks kernel
2.3 ) Booting Linux-i386 [b]zImage
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
1.0 ) Boot sectors
 These boot sectors are mostly designed for floppy use, the exceptions
 being the MinixFS and Master boot sectors.
 The makeboot program makes them very easy to install just format the
 disk add the correct filesystem then run a command like ...
 $ makeboot minix /dev/fd0
 As far as I know all boot sectors and programs are 8086 clean, with
 the exception that, obviously, the Linux-i386 loader needs access to
 extended memory.
1.1 ) Master boot sector
 This MBR is a very simple one with no frills by default.
 The actual code is less that 254 bytes long so it can be used as
 an MBR for a disk with old style 'Disk manager' partitions.
 The code now only boots one of the last four partitions.
 Option 2 is a boot message that displayed as soon as the MBR loads.
 Option 3 is code to accept a keypress from the user to select which
 partition to boot (or the floppy).
1.2 ) Dosfs boot sector
 Install with makeboot, there is also a version for 16 bit FAT
 filesystems for big floppies (eg LS-120 disks) or hard disk
 partitions. This boot sector loads and executes a binary BOOTFILE.SYS
 from the root directory of the floppy. The file can be any length
 and is loaded at 07ドルC00. Because of the load address this boot sector
 can be configured to load another boot sector, for example LILO can
 be succesfully used in this way.
 Note this boot sector loads the executable 1 sector at a time, as far
 as my testing has gone this is only significant on 8086 machines, all
 others (286 8Mhz +) are fast enough to keep up at a 1-1 interleve.
 But some versions of superformat can defeat this because they do
 not correctly calculate intersector gaps. I suggest using fdformat
 as this uses a 'safe' layout for standard 1440k disks.
1.3 ) Minixfs boot block
 This boot block has varients for floppy and harddisk and works similarly
 for both. For the hard disk it must be installed in the partition boot
 block with a normal MBR in sector zero of the disk. This boot sector can
 be installed with makeboot or simply by copying the 1k file to the start
 of the partition (or floppy) to be booted.
 The sector looks for a file or directory called 'boot' if it's a
 directory it loads that and does the search again. When it finds a
 file it loads it at location 10000ドル and executes it, note this
 is limited to a file size of 519k.
 There is also support for a helper boot which mean this is the only
 boot sector able to load an ELKS image (almost) directly.
1.4 ) Tar boot sector
 This boot sector converts a tar file with a GNU Volume label into a
 bootable floppy image. The boot sector loads and executes the first
 item in the tar file after the label:
 $ tar cvfV the_file.tar ENIAC monitor.sys item2 item3
 $ makeboot tar the_file.tar
 $ cp the_file.tar /dev/fd0
 This sequence makes a bootable floppy that tar sees as a normal labeled
 tar file but when booted from will load and execute 'monitor.sys' at
 location 00800ドル (Yes thats 2k!)
 Warning: the tar boot sector moves the BPB to the location 666ドル.
1.5 ) Skip boot sector
 This bootsector displays a message then loads and executes the hard disk
 MBR at location 07ドルC00
1.6 ) Panic boot sector
 Displays the message 'PANIC! NO OS Found!' (or the message specified
 on install) and freezes.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
2.1 ) Booting i86 standalone executable
 All the boot sectors (dos, minix, tar) check for a ELKS-i86 magic number
 at the start of the file they load and will correctly set the segment
 registers before calling. The executable should be a 'standalone'
 executable compiled with 'bcc -Ms ...' or similar.
2.2 ) Booting Elks kernel
 Only the minix boot sector can directly boot an elks kernel and even that
 needs a helper function because of the complexity. The helper is called
 'minix_elks.bin' and needs to be copied onto the disk as '/boot/boot'
 with the ELKS image copied on as '/boot/linux'. This works, with the
 correct boot block, on either floppy or harddisk.
2.3 ) Booting Linux-i386 [b]zImage
 None of the boot blocks can _directly_ boot a Linux-i386 kernel the
 program 'monitor.sys' must loaded by the boot sector and this can
 load a zimage or bzimage from an MSDOS, Minix or Tar floppy. It can
 also load the image from a minix hard disk filesystem.
 This example is for and MSDOS floppy, Tar is very similar except that
 'monitor.sys' must be the first file in the tar and can have any name.
 Note also for a tar file the 'ramdisk.gz' file must start on the first
 disk but can extend across as many floppies as is needed.
 $ mformat a:
 $ makeboot dos /dev/fd0
 $ mount -t msdos /dev/fd0 /mnt
 $ cp monitor.sys /mnt/bootfile.sys
 $ cp /usr/src/linux/arch/i386/boot/zImage /mnt/vmlinuz
 $ echo 'root=/dev/ram ramdisk_file=ramdisk.gz mem=80M' > /mnt/vmlinuz.cfg
 $ cp /archive/ramdisk.gz /mnt/ramdisk.gz
 $ umount /dev/fd0
 The stuff about ramdisk is only if you want an init ramdisk. If
 the ramdisk isn't on this floppy monitor.sys will ask for the
 right floppy. If you specify multiple ramdisk files then will be
 concatenated and passed to the kernel as one ramdisk, each file 
 can be on a different floppy.
 If the file isn't called 'vmlinuz' you can still boot it by typing "=linux"
 at the prompt '>' where 'linux' is the name of the bzImage file.
 Escape or ^C will interrupt the boot and drop you to the '>' prompt.
 ^C at the '>' prompt will reboot
 A file called 'help.txt' will be displayed upto the first line that starts
 with a '%', chunks after that (seperated by '%'s) will be displayed when
 the user presses a function key, home, page up or page down.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Robert de Bath <robert$@debath.co.uk>