MBR and Windows Boot Sectors

There are web pages on both the MBR and boot sectors for DOS 6.22 and some that discuss DOS 7 (Windows 95 OSR1) but I am not aware of any that discuss later versions with unassembled code. The pages below discuss the PC boot sequence but with special emphasis on the Windows 95 (OSR2) MBR and boot sectors which use Interrupt 13 extensions and new system indicators (partition types). Both the MBR and boot sector program codes are unassembled and commented. Windows 98 SE has also been added with topics not covered previously. Links on each page are provided to validate the information presented as well as to list sources that offer additional details.

These pages had their start with a need to learn about any problems with installing a larger hard drive and later by a discussion at a computer group of a problem with booting multi operating systems (Win 95,98 and DOS 6.22 among others) on a PC. Research on these problems led to a PowerPoint presentation that I delivered and then the material below.

All links for each page are listed at the bottom of the page with a description so that if a link has been changed there should be enough information to do a search for the page. Some pages may no longer exist.


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This page was created on 16 December 2000, last updated on 22 December 2004.