Until very recently - and it's still the case w/most PCs - it
hasn't been possible to boot from a USB device (which most
external HDs are). With the advent of eSATA (External SATA)
connectors on backpanels (perhaps on an expansion card),
external enclosures for SATA HDs are practical and meet
ATA specs.
No, only on newer ones, whose boards bios support it and
recognize the external thing.
Keep in mind that "boot" doesnt necessarily mean FINISH
booting, that depends on what the OS supports. For example,
a board might boot a SD card fine but WinXP may not like
that.
