I’ll soon have the opportunity to scavenge a bunch of computers being replaced at a local H.S. (Yes, they literally just throw these things away, and they’re decent systems). So I’m going to use one as a linux-only system, but I want to know if I can use another HDD on my current system without actually installing it internally. I’m not really sure why I want to know this, but I don’t and it’s bugging me.
So, is there a way to install a 2nd HDD and literally leave it outside the tower?
Thanks
Well, the proper way to do that would be to get an external USB/Firewire enclosure and put it in there.
I’m also almost certain that unless you buy some IDE controller cards, your PC has enough room inside it for all the drives you can add (probably a max of 4, optical drives included).
Of course, if you don’t care at all about that, and are in to doing things for no reason, then… sure, why the heck not? Route an IDE ribbon cable and a power cable outside your case, hook it up and leave it there.
I did that with an MFM or RLL drive from a 286 I was trying to make work in my old 486 when all reachable bays were full. (Yes, I know that would never work now. ) 1/2 way through the operation it fell off the footstool I had placed next to the box, and shorted the circuit board on the bottom of the drive against the PC case. The PC shut down in a shower of sparks, and despite hating Compaq for their proprietary everything, I was very impressed that after some intense swearing and removing the useless drive, the PC continued to work fine for years.
Depending on what you want to do, a drive bay caddy might also be a solution - OK, it’s sort of internal, but I get the impression that maybe what you’re wanting to do is to be able to switch between several different additional hard drives with relative ease - a removable hard drive caddy will do this (but it won’t be hot-swappable like, say, a USB hard drive)
I hadn’t even thought of using multiple secondary HDDs. But I am now. Thanks for yet another idea. 
Just remember that you cannot change drives without powering down. ATA is not a hot-swappable interface. You can hot-swap (sort of) with an external USB box and a caddy, though. Just stop the device under Windows or unmount under *nix and power off the box. Swap drives and power up. The new drive will be recognized immediately. Works fine for me.