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The boot code in the VBR can assume that the BIOS has set up its data structures and interrupts and initialized the hardware. The code should not assume more than 32 KB of memory to be present for fail-safe operation; [1] if it needs more memory it should query INT 12h for it, since other pre-boot code (such as f.e. BIOS extension overlays, encryption systems, or remote bootstrap loaders) may ...
boot.xxyy – these 512-byte files are backups of boot sectors, either the master boot record (MBR) or volume boot record (VBR), created when LILO overwrites a boot sector. xx and yy are the major and minor device numbers in hex; [ 5 ] for example, the drive sda has numbers 8, 0, hence its MBR is backed up to boot.0800 while the partition sda3 ...
In computing, the BIOS parameter block, often shortened to BPB, is a data structure in the volume boot record (VBR) describing the physical layout of a data storage volume. On partitioned devices, such as hard disks, the BPB describes the volume partition, whereas, on unpartitioned devices, such as floppy disks, it describes the entire medium ...
The MBR sector may contain code to locate the active partition and invoke its volume boot record. A volume boot record (VBR) is the first sector of a data storage device that has not been partitioned, or the first sector of an individual partition on a data storage device that has been partitioned. It may contain code to load an operating ...
The first reserved sector (logical sector 0) is the Boot Sector (also called Volume Boot Record or simply VBR). It includes an area called the BIOS Parameter Block ( BPB ) which contains some basic file system information, in particular its type and pointers to the location of the other sections, and usually contains the operating system's boot ...
To enable booting without the requirement either for a mass storage device or to write to the boot medium, it is usual for the boot program to use some system RAM as a RAM disk for temporary file storage. As an example, any computer compatible with the IBM PC is able with built-in software to load the contents of the first 512 bytes of a floppy ...
The MBR boot code and the VBR boot code are OS-specific. In Microsoft Windows, the MBR boot code tries to find an active partition (the MBR is only 512 bytes), then executes the VBR boot code of an active partition. The VBR boot code tries to find and execute the bootmgr file from an active partition. [3]
If the loaded boot sector is a PC DOS 3.3 (or newer) VBR, the requirements are slightly relaxed. The system files still have to be stored in the first two root directory entries on the disk, but the VBR will use only the first entry to load the first three sectors of IBMBIO.COM into memory and transfer control to it.