SATA internal disk and external drive - device changes

[Ed Jabbour]

Internal SATA drive designated as sdax.  I attached an external hard drive 
enclosure via USB.  Instantly recognized as sdb.  I formatted the external 
and successfully transferred files back and forth.  However, on a reboot with 
the external left on, I have the internal as sdbx and the external as sdc and 
sdc1.  Turned the external off and rebooted and I get sda and sdb.  Any 
advice, hints, pointers, etc. appreciated.  Relevant fstab entry:

/dev/sdb1 /mnt/external ext3 user,atime,noauto,rw,nodev,noexec,nosuid 0 0

Lastly, the external is one partition; I thought so, anyway.  Why sdb and 
sdb1?  sdb won't mount - wrong fs type, bad superblock stuff.  Did not format 
correctly?