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I do not understand why my partitions always start on absolute sector 63. What is the purpose of sectors 1 through 62? I understand sector 1 is the MBR but what about the rest? Thanks!

coeergo
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  • In LBA, the MBR is "sector 0", not sector 1. "Track 0" (for want of a better word as this has no real meaning anymore) goes from 0 to 62 in LBA, where the next track starts at sector 63 (or 1 to 63 in CHS, where the next track starts at 1, but on a different head or cylinder). – David Tonhofer Aug 13 '16 at 19:24

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Sector 0 is the MBR. Sectors 1 to 62 are empty so that the file system starts on an aligned boundary. Newer versions of Windows start at the 1MB boundary.

Chris S
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  • From [Wikipedia CHS](https://en.wikipedia.org/wiki/Cylinder-head-sector) entry: _"For physical disk geometries the maximal sector number is determined by the low level format of the disk. However, for disk access with the BIOS of IBM-PC compatible machines, the sector number was encoded in six bits, resulting in a maximal number of 111111 (63) sectors per track. This maximum is still in use for virtual CHS geometries."_ So "aligned" means "Starts on a new track, assuming 63 sectors per track" (Why not 64? Maybe because sector 0 of each track was used by the hardware for storing ECC stuff?). – David Tonhofer Aug 13 '16 at 19:13
  • So this means MBR is "cylinder 0, heade 0, sector 1" in CHS addressing or "sector 0" in modern linear [Logical Block Addressing](https://en.wikipedia.org/wiki/Logical_block_addressing). – David Tonhofer Aug 13 '16 at 19:21
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    Note that sectors 1..62 are used to hold bootloader code, at least for grub/grub2. The "core.img" (stage 1.5) resides in these sectors. It is able to find the partition holding the `/boot` directory and understands enough of the file system to grab files therein and branch into them. See: [grub2](https://en.wikipedia.org/wiki/GNU_GRUB#GRUB_version_2_.28GRUB.29) – David Tonhofer Aug 13 '16 at 19:30