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I just plugged my iPhone into my new mac (previously it was managed using itunes on a PC)

I just want to delete some songs that are on the iPhone.

It seems I can't press delete on the songs in iTunes when the phone is connected.

When I select Manually manage my songs and videos it prompts "the iphone is synced with another itunes library. Do you want to erase this iPhone and sync with this iTunes library?"

I don't understand because it was manually managed on my PC not synced to a library. Also the prompt isn't very helpful, what does "erase this iPhone" mean? Delete everything? Just music and videos?

If I check "Manually manage my songs and videos" and receive the prompt which says it will "erase this iPhone" what will it actually erase? Is it just the songs and videos?

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3 Answers 3

up vote 6 down vote accepted

The first part of the sync error message means exactly what it says - your iPhone can only be associated with a single iTunes library. The second half is tricky for people that are analytical, but for most users it's meant to make them want to back up their phone before they

Regardless of how you choose to copy your content (sync manually or automatic) it maintains a connection to a single library to which is is allowed to copy music/films/apps etc to and from, and where backups/restores etc can be made. Unless you know exactly what was synced - you could be inadvertently erasing some content hence the scary general error message.

If you introduce your iPhone to a new iTunes library, then it can remove any content that is associated with the previous one. Assuming you still have access to the old one you can copy the files from one computer to another to enable you to sync them back again after, or you can transfer the purchases to the new iTunes library assuming it has been authorised using the same Apple ID. This is an attempt to limit unauthorised copying of music and other content etc, otherwise you could happily take your phone or iPod around to all your friends laptops and merrily copy all their stuff onto your device, where you could then happily sync it back to your iTunes library at home.

Other phone content, like emails, contacts, settings should remain unaffected, as these are not held within the iTunes library (even if you have set iTunes to be the sync mechanism for putting them on your phone, they belong outside of the library.

Rule of thumb: if the original iTunes copied the content on in the first place, it will be removed. It won't just wipe the whole phone, just what came from iTunes.

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1  
I don't mean to be rude, but it's quite amusing because even you can't answer my simple question, "what does 'erase this iPhone' mean". I don't really appreciate the this is an "attempt to prevent unauthorised copying of music", but considering my situation, how do I migrate to my new PC? I don't care about the music or videos, but I DO care about all the other content on the phone. I just want a straight answer on what I will lose by selecting "erase this iPhone". Surely I can de-link the phone from the old computer and lose whatever music, then sync to the new computer? –  applenewbie Sep 24 '13 at 13:01
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I have rewritten the comment I intended to put here many times. I will settle with simply stating that I refer you to my answer, which I feel answers your question perfectly well, as evidenced by the upvotes. If you are not satisfied with it, then please vote it down - that is the generally accepted way to pass your verdict on any particular contribution. Perhaps someone else could spend some of their free time in trying to help you in exactly the way you wish to be helped. –  stuffe Sep 24 '13 at 13:19
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@applenewbie The simple answer is that syncing is complicated. You can simplify things by making a full backup and then experimenting. When you jump and let the "new" iTunes erase what it wants, then you'll know what it thought needed to be erased. –  bmike Sep 24 '13 at 14:40
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@stuffe, i'm not having a go at you on a personal level. Yes, backing up the phone and 'seeing what happens' works but what a pathetic solution, and waste of time. A google search for the terms 'erase this iPhone' will reveal that i'm not the only person who thinks the text on the dialog is vague and unhelpful. Writing code to provide a more specific erase message is not impossible, it just hasn't been implemented (or, I assume, seen as a priority) by Apple. –  applenewbie Sep 25 '13 at 10:17
    
I can't help how Apple word things, but I can explain what it means, and I hopefully have done so for you. –  stuffe Sep 25 '13 at 10:18

The message is wrongly worded — it doesn't erase the entire iPhone, but only content synced from another library which is now being replaced.

Let's say that you had synced music, photos, apps and ebooks from iTunes on machine 1. Now you try to sync music from iTunes on machine 2. It deletes only the music on the iPhone, and then syncs the music over. It does not touch the other content types (photos, apps, etc) because you are not syncing those.

This is the behavior in iOS 6 -- I don't know about 7.

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In my case I plugged my iPhone into the new iTunes then clicked 'sync' for the music only and it deleted all the music that was on my iPhone and replaced it with all the music that was in iTunes.

This seemed to work fine and DID NOT delete my contacts, texts, emails, apps, etc., etc. Although in my case I sync those things to iCloud so I cannot speak for iPhones that are not synced to iCloud. Maybe iTunes will delete this stuff, although based on the fact it did not delete my photos and etc. I would say this is unlikely.

I know it's not a full answer, but I am confident if you sync the music only the message “Do you want to erase this iPhone and sync with this iTunes library” will only apply to the music on the device. Just make certain you have not clicked 'sync' on any other tab such as contacts.

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