Extended boot record

EBRs have essentially the same structure as the MBR; except only the first two entries of the partition table are supposed to be used, besides having the mandatory boot record signature (or magic number) of at the end of the sector. : Values The following are general rules that apply only to values found in the 4-byte fields of an EBR's partition table entries (cf. tables above). These values depend upon the partitioning tool(s) used to create or alter them, and in fact, most operating systems that use the extended partitioning scheme (including Microsoft MS-DOS and Windows, and Linux) ignore the "partition size" value in entries which point to another EBR sector. One exception is that value must be one or greater for Linux operating systems. The first entry of an EBR partition table points to the logical partition belonging to that EBR: :*Starting sector = relative offset between this EBR sector and the first sector of the logical partition ::Note: This is often the same value for each EBR on the same hard disk; usually 63 for Windows XP or older. :*Number of sectors = total count of sectors for this logical partition ::Note: Any unused sectors between EBR and logical drive are not considered part of the logical drive. : == Examples ==

This shows an extended partition with 6,000 sectors and 3 logical partitions. Remark: Neither a tiny extended partition with only 3 MB nor a hard drive with 20 sectors per track are realistic but these values have been chosen to make this example more readable. Snapshot The following output of a command line tool shows the layout of a disk with two logical drives. Details for the FAT and NTFS partitions stripped, the line annotated with Linux is /dev/hda6 with an extended file system. The begin of /dev/hda5 shows that the involved operating systems PC DOS 7, Windows NT, and Debian do not insist on any extended partition alignment with a gap: \\.\PHYSICALDRIVE0 (assuming geometry CHS 99999 255 63) id. [3189-3188] MBR CHS 0 0 1 at 0, end 0 0 1, size 1 unused CHS 0 0 2 at 1, end 0 0 63, size 62 1:*06: CHS 0 1 1 at 63, end 260 254 63, size 4192902 bigFAT 2: 05: CHS 261 0 1 at 4192965, end 757 254 63, size 7984305 => EXT 3: 17: CHS 758 0 1 at 12177270, end 1522 254 63, size 12289725 NTFS 4: 1C: CHS 1523 0 1 at 24466995, end 1825 254 63, size 4867695 FAT32 (extended offset 4192965) total 29334690 => EXT CHS 261 0 1 at 0, end 261 0 1, size 1 5: 06: CHS 261 0 2 at 1, end 384 254 63, size 1992059 bigFAT 6: 05: CHS 385 0 1 at 1992060, end 757 254 63, size 5992245 => EXT (extended offset 6185025) total 7984305 => EXT CHS 385 0 1 at 0, end 385 0 1, size 1 unused CHS 385 0 2 at 1, end 385 0 63, size 62 6: 83: CHS 385 1 1 at 63, end 757 254 63, size 5992182 Linux 7: 00: CHS 0 0 0 at 0, end 0 0 0, size 0 unused total 5992245 bigFAT CHS 0 1 1 at 63, end 260 254 63, size 4192902 PC DOS 7 (cluster size 64, number 65506) total 4192902 NTFS CHS 758 0 1 at 12177270, end 1522 254 63, size 12289725 [1C81-013D] (cluster size 8, number 1536215) total 12289725 FAT32 CHS 1523 0 1 at 24466995, end 1825 254 63, size 4867695 [C417-9E22] (cluster size 8, number 607271) total 4867695 bigFAT CHS 261 0 2 at 4192966, end 384 254 63, size 1992059 FAT SWAP (cluster size 32, number 62236) total 1992059 For another example see the "Linux Partition HOWTO".{{cite web == Footnotes ==