Hi all, Some of you here are working on boot sectors and related stuff. Today I learned about a fact that I didn't know about, which you can consider interesting -- of course, if you didn't know it before.
It is known that hard disk partitions starting beyond 1024th cylinder may be non-bootable, due to limitations of BIOS (no INT 13h extensions), Master Bootstrap Loader code in MBR (old MBRs cannot use INT 13h extensions), or partition's boot record and OS kernel (INT 13h extensions unsupported in older versions of DOS etc.) Today I encountered a BIOS which does have INT 13h extensions, but makes booting an LBA-enabled OS (Win98SE, but it is irrelevant) using an LBA-enabled MBR (no matter what sort of) from a partition starting beyond 1024th cylinder impossible. Apparently, before passing control to the Master Bootstrap Loader, this BIOS scans the Partition Table for active partition, and if it requires LBA to boot, treats the entire disk as non-bootable and asks for a bootable diskette instead of running the Master Bootstrap Loader. (This is based on observation, not on BIOS code analysis, but I cannot find any other reasonable explanation and do not want to waste my time with a disassembler.) So far, I only saw a BIOS which refused to pass control to the Master Bootstrap Loader when there is no partition marked as active (even if the Partition Table is valid). This one is much worse. The observed behavior makes these boot managers, which update the Partition Table to mark the partition selected by the user as active, partially useless. Even if the previously selected partition starts below 1024th cylinder and the boot manager gets control over the system, when you select one which starts beyond it, at next boot you have to use a floppy. This affects also BootEasy written by FreeDOS FDISK (if the current version supports INT 13h extensions -- that one which I have does not, but it is rather old). The BIOS described here is SystemSoft MobilePRO BIOS v1.01 in a California Access notebook model CA 6700. (It is my friend's machine. I would not ever buy something like that.) Regards, Michal -- Michal H. Tyc, BTTR Software (http://www.bttr-software.de/) ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Freedos-kernel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/freedos-kernel
