What are the limitations imposed by an external USB/Firewire HDD ?

[mullardel34]

Recalling the buyer reviews that I have read so far, most external enclosures could use improvement. Even so, everyone is out to purchase one. A flood of these enclosures hit eBay, so I bought two of reasonable quality. But there are many questions I have about shopping for an enclosure (and card), and about using one.

What are the limitations imposed by an external USB/Firewire HDD & enclosure ?
How restricted is the use of the harddrive ?
Can you mirror another harddrive with Norton Ghost ?
Can you restore a damaged OS with backups from the external enclosure ?
Can you boot from Firewire or USB 2.0 ? What board, what BIOS, what enclosure ?
What software is best with an external enclosure ?
How does the enclosure behave when installed ?
Does it need to be Removed (at the tray icon) in order to reboot ?
What chip is best in each type of enclosure; USB 2.0, Firewire, and COMBO ?
What Firewire, USB 2.0, and COMBO cards are un-installable ?
What chipsets should be sought after when buying such a card ?
And the Firewire cable, 6-pin or 4-pin, what's the difference ?

Any comments that apply would be appreciated, and if I missed something, please post it.

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For a quick look at external enclosures, check this link. There are many brands, lots of pictures, and the descriptions will usually name the chipsets used.

http://www.dealsonic.com/dealsonic/exen.html

Thanks in advance.