Will using an external hard drive cause me to have duplicate files on my itunes library?

Question

I put all my ITUNES MEDIA folder on my external hard drive from my older computer.. I recently bought a new computer and installed Itunes. I synced some of my Itunes purchased songs back on by using my Ipod.. however the songs I ripped from my cds are still not reinstalled in my library.. I will have to use my external hard drive or re rip those.. and there are a lot of them.. since I have already replaced some of the ones I purchased back on using my Ipod will it duplicate them if I use the prefrences method and return them all from my external hard drive? If i delete my files that I have already returned on my new computer before using my external will Itunes remember which are Itunes purchased music and which arent as well>??? also how exactly do you move music from an external? just plug it in and click the prefrences box about syncing files and keeping Itunes library organized?? any other thing to click?

Answer 1

An iTunes library consists of both the media and the database that knows which files are in the library and hold details of ratings, playcounts, playlist membership and other details not stored in each file's metadata.
Depending on how you have moved content to your external drive you may find you are only moved the media, but not the database. If you import this media into a new library it will work, but your library will be seen as "new" with respect to any devices that you have and iTunes will want to erase and reload them, losing you current selections, settings and data on the device.
These are two possible approaches that will normally work to move an existing library to a new computer.
Method 1
Backup the library with this User Tip.
Deauthorize the old computer if you no longer want to access protected content on it.
Restore the backup to your new computer using the same tool used to back it up.
Keep your backup up-to-date in future.
Method 2
Connect the two computers to the same network. Share your <User's Music> folder from the old computer and copy the entire iTunes library folder into the <User's Music> folder on the new one. Again, deauthorize the old computer if no longer required.
Both methods should give the new computer a working clone of the library that was on the old one. As far as iTunes is concerned this is still the "home" library for your devices so you shouldn't have any issues with iTunes wanting to erase and reload.
I'd recommend method 1 since it establishes an ongoing backup for your library.
If you have an iOS device that syncs with contact & calendar data on your computer you should migrate this information too. If that isn't possible create a dummy entry of each type in your new profile and iTunes should offer to merge the existing data from the device into the computer, otherwise the danger is that it will wipe the information from the device.
If your media folder has been split out from the main iTunes folder you may need to do some preparatory work to make it easier to move. See make a split library portable. Alternatively you could copy over the iTunes folder and make sure your external drive has the same drive letter on the new system as the old, however moving the library into a portable form will make every subsequent move that much easier.
Should you be in the unfortunate position where you are no longer able to access your original library, or a backup of it, then see Recover your iTunes library from your iPod or iOS device for advice on how to set up your devices with a new library with the maximum preservation of data.
tt2