Windows always assigns the active OS with C: and only one instance of that letter can ever be used in Windows.  If you do keep both drives attached, whatever is booted will be C: and the other one will show up as the next available letter - it will always be like that because that running OS will need to assign the other drive with some letter.  If you boot into the other drive, it will then be C and the other will show up as some other drive letter - this does not change the drive letter on that actual drive, it's just how that booted OS handles it.

Regardless, I don't recommend keeping both drives attached at the same time, especially right after the clone process... Before you attempt to boot the clone, you should always remove the original and put the clone where it was and boot it.  This is really for BIOS dependencies... if the bios sees them as the same hard drive it can get confused and may try to update the bios UEFI bootloader.  Once it's been booted separately, you're probably OK to attach both, but it really depends on how your bios can handle them both being attached as they are technically the same drive (down to the UUID when you clone).   

A clone is not really meant to be a backup/recovery replacement.  Feel free to clone, but keep the disk unattached unless it's needed.  Otherwise, stick with backup and recovery.  Once you make a clone, it's old after a day or 2 anyway, so that's why backup/recovery can be much better as it can be used to backup continuous changes and recover to a more recent point in time.  

You can never boot a clone that is attached to USB either - this is Windows limitation. 

Thanks for the reply.   Yeah, I know the clone is old after only a short time, but I have a bit of a different situation.  Two computers side by side.  My i5 I use for internet surfing, playing with different programs etc ....   The i7 is for my video editing and I don't add many programs to it.  Video files and program editing files are kept on a seperate drive. I also use a KVM switch so I can switch to two monitors and back again without turning off my i5 if I need more real estate to edit the video.  The i5 is the one that gets loaded with lots of stuff all the time.

In fact, I kind of like the idea that the clone is a fresh install with programs.  Less likely to be a mess.

Joe West wrote:

In fact, I kind of like the idea that the clone is a fresh install with programs.  Less likely to be a mess.

You could do exactly the same with a full disk mode backup. I see no advantage to cloning.

Ditto.  Backup/restore actually has the advantage as it gives you backup that you can use at any point in time.  Cloning is "on the fly" and if something goes wrong, you're outta luck.  Even if you do like cloning, I'd still recommend taking a backup first - it's your saving grace.  And as Tuttle mentioned, the results are exactly the same - a restored hard drive to the state it was in at the time it was backed up. 

I guess I don't really understand the backup concept. That's one reason I choose clone.  I mean I know you can do differential, or incrimental, but to be honest, I don't really understand the difference.  I can read the difference over and over, but I must have a mental block.

So I make a backup of my "C" drive to another hard drive, ( this is a compressed unusable file as it is)   then, if my "C" drive fails,  I have to have yet another, third new drive to install blank in my computer as my new "C" drive, and then restore to that drive from the backup drive file?

But how can I do anything on that computer, it doesn't have an operating system on it.  Does the backup drive restore to itself?   What if there isn't room for both the uncompressed files and the backup copy.   See, I just dont' understand.

The backup copy will also put the boot and operating system on the new drive?

Now a clone, if something happens to my "C" drive, I simply put the clone in it's place, done deal.  Then I'm at my leisure to get another drive to make my new clone.  Seems the down time is non existant.

When you back up, don't you have to have a copy of the software you used handy to restore?  Also, does a copy of that software have to be on the new drive?   I guess I never gave backup a chance cause I didn't see an advantage to look into understanding it.  I'll read more about that option.

What most of us do is to create backups to an external HD, say a USB HD. If your system disk fails, you could remove it, install the replacement drive, boot from the ATI Rescue Media, and resore the backup image to the new drive.

Create the ATI Rescue Media now, and make sure your PC can boot from it.

check this out...

1540: Difference between Backup and Disk Clone

the meat of that KB article is...

In general, disk clone is a one time operation designed to clone one disk to a different one for the purpose of migrating to a larger hard drive or to a new machine.

A backup operation offers greater flexibility as a backup strategy:

• Backup can be scheduled (e.g. regular automatic backups that require no user interaction);
• Backup changes can be appended incrementally or differentially (i.e. after a full backup, subsequent backups will take less time and occupy less space than the first one);
• Backups allow you to keep several versions of the backed up data and you can restore to one of the previous versions (e.g. you can keep backups from one, two and three weeks ago on the same disk and you can recover the backup from the moment that you need);
• Backup can be mounted and searched through (e.g. if you want to quickly find, view and copy a file from it).

Either way (backup and recovery of the entire disk or disk clone) you can transfer the whole operating system and installed programs to a new disk.