Paritioning scheme on MBR disk doubts

[Christian Groessler]

On 8/27/21 6:48 AM, Ralf Mardorf wrote:
> On Thu, 26 Aug 2021 20:53:25 +0200, Christian Groessler wrote:
>> If I remember correctly, an extended partition can also only hold 4
>> partitions. Of which one in turn can again be an extended partition
>> which can hold 4 partitions. Of which one in turn can again be an
>> extended partition... etc
> That's incorrect.
>
> "Master Boot Record (partition table)
>
> In the MBR partition table (also known as DOS or MS-DOS partition
> table) there are 3 types of partitions:
>
>      Primary
>      Extended
>          Logical
>
> Primary partitions can be bootable and are limited to four partitions
> per disk or RAID volume. If the MBR partition table requires more than
> four partitions, then one of the primary partitions needs to be
> replaced by an extended partition containing logical partitions within
> it.
>
> Extended partitions can be thought of as containers for logical
> partitions. A hard disk can contain no more than one extended
> partition. The extended partition is also counted as a primary
> partition so if the disk has an extended partition, only three
> additional primary partitions are possible (i.e. three primary
> partitions and one extended partition). The number of logical
> partitions residing in an extended partition is unlimited. A system
> that dual boots with Windows will require for Windows to reside in a
> primary partition.
>
> The customary numbering scheme is to create primary partitions sda1
> through sda3 followed by an extended partition sda4. The logical
> partitions on sda4 are numbered sda5, sda6, etc. Tip: When partitioning
> a MBR disk consider leaving at least 33 512-byte sectors (16.5 KiB) of
> free unpartitioned space at the end of the disk in case you ever decide
> to convert it to GPT. The space will be required for the backup GPT
> header." -
> https://wiki.archlinux.org/title/partitioning#Master_Boot_Record_(partition_table)


The first sector of an extended partition has the same layout as the MBR.