I have a Thinkpad with Windows 7. Last time I installed an Ubuntu/Windows dual boot, Windows was never same after and regularly got corrupted so this time, I installed Ubuntu on a separate external hard drive.

I took a 500 GB external hard drive and used Windows to shrink the partition on it to 400 GB, freeing 100 GB to install Ubuntu.

Then I modified the booting priority of my computer to boot from the external hard drive if present.

Then, I installed Ubuntu desktop on the external hard drive using a DVD, picked the most simplistic partitioning scheme I could get away with (didn't go auto as it didn't include the external hard drive as a choice) and voilà.

Fast forward some time and I'm trying to refresh my understanding of Linux partitions to install a bunch of servers, so I'm looking at the current partitioning scheme on my external hard drive and find the boot partition puzzling...

sda is my integrated hard drive with Windows 7. sdb is my Ubuntu desktop external hard drive.

Running parted on sdb, I get this:

(parted) print                                                            
Model: WD My Passport 0740 (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End    Size    Type      File system     Flags
1      1049kB  393GB  393GB   primary   ntfs            boot
2      393GB   500GB  107GB   extended
5      393GB   425GB  32.8GB  logical   linux-swap(v1)
6      425GB   500GB  74.6GB  logical   ext4

At this point, I'm wondering why the ntfs partition is flagged as "boot" and not my ext4 partition which is the partition that contains / (and by extension, /boot since it's not on its own separate partition).

Looking at mtab only confirms what I already know:

eric@eric-ThinkPad-W530:~$ sudo cat /etc/mtab
/dev/sdb6 / ext4 rw,errors=remount-ro 0 0
proc /proc proc rw,noexec,nosuid,nodev 0 0
sysfs /sys sysfs rw,noexec,nosuid,nodev 0 0
none /sys/fs/cgroup tmpfs rw 0 0
none /sys/fs/fuse/connections fusectl rw 0 0
none /sys/kernel/debug debugfs rw 0 0
none /sys/kernel/security securityfs rw 0 0
udev /dev devtmpfs rw,mode=0755 0 0
devpts /dev/pts devpts rw,noexec,nosuid,gid=5,mode=0620 0 0
tmpfs /run tmpfs rw,noexec,nosuid,size=10%,mode=0755 0 0
none /run/lock tmpfs rw,noexec,nosuid,nodev,size=5242880 0 0
none /run/shm tmpfs rw,nosuid,nodev 0 0
none /run/user tmpfs rw,noexec,nosuid,nodev,size=104857600,mode=0755 0 0
none /sys/fs/pstore pstore rw 0 0
systemd /sys/fs/cgroup/systemd cgroup rw,noexec,nosuid,nodev,none,name=systemd 0 0
gvfsd-fuse /run/user/1000/gvfs fuse.gvfsd-fuse rw,nosuid,nodev,user=eric 0 0
/dev/sdb1 /media/eric/My\040Passport fuseblk rw,nosuid,nodev,allow_other,default_permissions,blksize=4096 0 0

My lack of understanding concerning this is not vital to anything (this is only my development desktop partition), but somehow annoys me. Any insight that could shed some light on this would be welcome.