People that want to be able to boot many systems, and can boot
only from a primary partition, and use one primary partition
for the OS/2 Boot Manager, have only 3 partitions left.
If some of these partitions start past the 1024 cylinder mark,
they might have no choice.
Typical scenario: MBR starts OS/2 BM. Then OS/2 BM starts the
desired system, either directly (e.g., DOS or OS/2) or using
another boot loader (e.g., LILO for Linux).
: If we really want to do allow it, we could just set the size of the raw
: extended partition to be 2 sectors (1 block), and mke2fs won't be able
: to make a partition on a partition that small.
No, because only 1 sector is guaranteed to be free. Writing a
block to /dev/hda4 might destroy the first sector of /dev/hda5.