Hi Bernd,
There is a INT 18h call. According to the BIOS boot specification [2] this may called by an IPL to indicate failure to boot. This might be something to investigate further. We do not have this in our IPL...
Turns out we have this, but not in the default IPL (bootnorm.asm), but in booteasy [1]. So my idea is to transfer this INT 18H call over to bootnorm.asm: - display message if no partition is active or VBR misses boot signature - wait a few seconds to make sure user sees the message, as some INT 18 implementations seem to clear the screen, maybe do not even work... - issue INT 18 - hope for the best - loop in case INT 18 returns Anything that speaks against this method? Any reason it is not in bootnorm.asm?
RBIL answers that:
INT 18 - DISKLESS BOOT HOOK (START CASSETTE BASIC) Desc: called when there is no bootable disk available to the system Notes: very few PCs other than those produced by IBM contain BASIC in ROM, so the action is unpredictable on compatibles; this interrupt often reboots the system, and often has no effect at all
In short, it is not expected to be of any use. I would avoid it.
some PC and XT clones had an optional IBM CASSETTE BASIC stored in the ROM, too. most BIOSes will display an error message similar to "NO BASIC", and either reboot or return to the caller.
PS/2 machines usually pop up a graphical box to the effect that the user should enter a floppy and press F1. Some clones display the message "No boot device available, strike F1 to retry, F2 for setup utility"
This might be what the boot sector was hoping for, but removing the 55AA magic and not having it run at all may make more sense.
network cards with their own BIOS can hook this interrupt to allow a diskless boot off the network (even when a hard disk is present if none of the partitions is marked as the boot partition)
SeeAlso: INT 2F/AX=4A06h,INT 86"NetBIOS",INT 2F/AX=4A06h,INT 2F/AX=4A07h
Regards, Eric
[1]: https://github.com/FDOS/fdisk/blob/3fc4785b49ac5af366e27804c132302423f07f19/SOURCE/FDISK/BOOTEASY/BOOTEASY.ASM#L179
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