Helping people with computers... one answer at a time.

Computers are configured to run off an internal C drive; and there is also the question of speed and convenience.

My HCL laptop's internal hard disk is dead. Can I use my external USB Seagate hard disk, 500 GB, as my internal hard disk? Can I install the operating system on it?

In this excerpt from Answercast #45, I look at the problems involved in trying to run an operating system off an external drive.

Running off external drive

The answer is it depends.


  • The external drive that you have uses a drive that is the same size as your internal drive (and I mean the same physical size; 2 1/2 inches I believe is what most of those drives are);

  • And the external drive uses the same interface (either IDE or SATA, as your laptop does, and again, it's probably SATA);

...then absolutely! You can remove the hard disk from the external enclosure, place it into your laptop, reinstall the operating system on it from scratch (by booting from your installation media or restoring from a backup) and you should be good to go.

But the important thing to realize are those two things:

  1. The actual drive (I'm not talking the enclosure; I'm talking about the hard disk that's inside that external drive enclosure) needs to be the right physical size so that it will fit inside of your laptop.

  2. And it needs to have the correct interface (so that the laptop will know how to talk to it).

Operating system on external drive

Now, if your question is, "Can you leave it as an external drive and have it be treated as if it were internal?"

The answer there is no.

  • It's either not possible physically (and by that, I mean there's no way to convince the machine that hey, this disk over here is the internal drive);

  • But it's also not something you want.

Hard drive speed

Realize that the speed with which the drive is accessed internally is significantly faster than the speed with which devices on USB buses are accessed:

  • So, you'll end up with a fairly slow machine;

  • And you'd have to carry this external box along with a laptop.

It just doesn't make a whole lot of sense. At that point, the right thing to do is to simply replace the internal drive in that laptop.

So, again, short answer, yes, as long it meets certain requirements.

End of Answercast #45 Back to – Audio Segment

Article C5717 - August 20, 2012 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

Ron Wall
August 21, 2012 10:36 AM

Running external hard drive when
Encountered virus and malware on my desktop dell
Will malware have Been transferred
To external drive?if so , how would I
Get rid of malware when reusing my
External drive on new computer?

Mark J
August 21, 2012 11:37 AM

If your computer has a virus, it's possible that the virus will also somehow be on the external drive. Run an AV scan or 2 on the drive before putting it into computer. If you plan to do a clean install of windows on the drive, this won't be necessary as the clean install would overwrite any malware.

August 21, 2012 3:34 PM

Laptop hard drive kaput? Perfect time to exchange for a solid state drive. Terrific speed increase. Prices have dropped to$80 to $100 for a 120 to 128 GB unit. Remember not to defrag the drive.

bob price
August 24, 2012 9:37 AM

I would not want to leave my ext ESATA backup drive as the primary, but I can easily enter Setup and change boot sequence. This sets the ESATA ext drive as first boot, and it boots as the new "C" drive, and the laptop does not know the difference. I do this a few times a year to ensure the bootable backup was successful, so yes, you can fool the laptop into thinking your ext drive is primary.

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