Master Boot Record and partition tables

Published on July 31, 2012

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In our earlier post describing Fastboot on our i.MX products, we passed the buck on how a Master Boot Record and partition table is constructed.

As shown in the Wikipedia article, there's a lot of legacy involved in this important data structure and we'll try to distill the important points here.

Includes Cylinder/Head/Sector (CHS) numbering for legacy systems,
Limited to four partitions and uses Extended Boot Records to define additional logical partitions within an Extended partition.

U-Boot supports supports five different partition types, although most builds support far fewer.

U-Boot also doesn't appear to use CHS addressing for anything.

The CHS address space is used for placement of EBRs and serves as a unit of allocation by fdisk as described in this post.

More to come.