Syncing behaviour/direction of individual content type in iTunes

[ralliart122010]

Hi fellows. I wish to clarify my understanding of how iTunes sync (overwrite) the individual content type on an iPod. The scenario is: when I sync an iPod with another new library, typically we will be prompted with the warning message, "this iPod is currently synced with another library. If you choose to sync it with this library, all the existing content will be replaced with the content on this library" (or some similar warning). My doubts are as follows:

Qn1. Am I right to say that, even if I click "okay" to that warning message above, the actual "replacing" doesn't start immediately as iTunes will wait for the user to select what subset of content he wants, & more importantly, for the user to click the "sync" button (near the bottom right of iTunes) before the actual erasing and replacing begins?

Qn2. Does iTunes treat each content type as separate libraries, i.e. in the context of "approving" iTunes's demand to overwrite the existing content on the iPod with content from iTunes own, current library, if the "sync" checkbox on the other content type's tab is unchecked, will that existing content type stored on the iPod be excluded from the erasing and replacing?

I understand this may be very confusing, so allow me to illustrate my question with a specific example:



If I choose to sync music from the current iTunes library to an iPod that was previously synced with another library, and I approved iTunes to go ahead and replace the existing music on the iPod with the music from the iTunes library but I have the "Sync Apps" checkbox unchecked, will the apps on the iPod be wiped? Similarly, if the "sync movies" checkbox on the Movie tab is unchecked, will the movies on the iPod be wiped when I allow iTunes to replace the music library on the iPod with the songs from iTunes?

Qn2a. If iTunes treat syncing each content type libraries on their own, are music and movies treated as one library?

Qn2b. What determines the initial "checked/unchecked" status of each of those check-boxes in the diagram above when an iPod that is synced with another library, is connected to iTunes for the first time?

In fact (this paragraph is not a qn; just a comment) I find the manner in which this is handled in iTunes to be inelegant. E.g. suppose in the context of qn2 iTunes treat all content type libraries as one unified library, and once I give iTunes the permission to erase the songs on the iPod with the songs from its current library but say I don't wanna replace the apps on the iPod with the apps from this iTunes library; neither do I wish to replace the podcasts on the iPod with the podcasts on this iTunes library. I can goto the "Apps" tab and uncheck "Sync Apps", but I could not goto the "Podcasts" tab and uncheck "Sync podcasts" without committing/applying the updated aps syncing conditions first. So if the "Sync podcasts" checkbox was checked for some reason, the podcatss on the iPod will be replaced with podcasts from the iTunes library without my "permission".

For those who are veterans with this sync-ing behaviour stuff, I sincerely hope to gain some insight as to how iTunes behaves (in these contexts above). Thanks n advance.

[ScoobZ]

Originally Posted by ralliart122010

Hi fellows. I wish to clarify my understanding of how iTunes sync (overwrite) the individual content type on an iPod. The scenario is: when I sync an iPod with another new library, typically we will be prompted with the warning message, "this iPod is currently synced with another library. If you choose to sync it with this library, all the existing content will be replaced with the content on this library" (or some similar warning). My doubts are as follows:

The part in bold answers your questions. All content will be erased, regardless of type.

Qn1. Am I right to say that, even if I click "okay" to that warning message above, the actual "replacing" doesn't start immediately as iTunes will wait for the user to select what subset of content he wants, & more importantly, for the user to click the "sync" button (near the bottom right of iTunes) before the actual erasing and replacing begins?

The erasing starts immediately.

Qn2. Does iTunes treat each content type as separate libraries, i.e. in the context of "approving" iTunes's demand to overwrite the existing content on the iPod with content from iTunes own, current library, if the "sync" checkbox on the other content type's tab is unchecked, will that existing content type stored on the iPod be excluded from the erasing and replacing?

No, it's all one library, music, podcasts, movies, etc. Just one library.

Now, all of the above assumes that the iPod is in auto sync mode. In order to sync different content with different iTunes libraries on different computers you want to put your iPod into manual management mode. Then you can manually sync music from one computer, movies from another, etc.

[ralliart122010]

Originally Posted by ScoobZ

...Now, all of the above assumes that the iPod is in auto sync mode...

Hi ScoobZ, thanx for ur speedy response. May I check with you" what do you mean by "in auto sync mode"?

[ScoobZ]

Originally Posted by ralliart122010

Hi ScoobZ, thanx for ur speedy response. May I check with you" what do you mean by "in auto sync mode"?

There are two types of syncing your iPod.

One is automatic where when you connect your iPod to your computer the syncing starts automatically. What gets synced depends one what you select to be synced, be it your entire library, just certain playlists, etc.

The other type of syncing is manual, also called manual management of music and other content. When your iPod is set for this method, nothing happens when you connect your iPod to your computer. To get content onto your iPod you use the drag/drop method of songs, lists, movies, etc.

The default setting for sync is automatic. If you want to change that, when your iPod is connected to your computer select it and then look at the Summary tab. In the Options section you will see a choice to Manually manage music and videos.

[ralliart122010]

That's the funny thing that occurred to me recently (& hence the reason I started this thread).

Background
My iPod is set to automatic syncing. All the "Sync so-&-so" in each tabs were checked, i.e. you can say it's "totally automatic syncing management". Recently, I migrated to an entirely new iTunes library (all properly tagged & organized) & hence I decided to "pair" my iPod with this new library.

The very 1st thing I do is launch iTune using the "Shift" key to initiate with the new library instead of the last-used old library. I also authorized the computer with my iTunes store account again. I also had this option, "Prevent...from syncing automatically" deactivated all along. Hence, when I plug in my iPod to this new library, no syncing commences automatically (which is expected behaviour; good).



And then I tried to do a "Transfer Purchases", because I wish to get whatever apps that are on the iPod into this new library. Realized it took too long, I abort the transfer and instead import the ipa files from the directory of my old library's "iTunes Music" folder into this new library. But anyway, here's where the behaviour of my iPod syncing deviates greatly from what you mentioned in your earlier post:

The "Sync Music", "Sync Apps", "Sync Movies", etc were unchecked by default when I click on my iPod Touch from the iTunes Source list. Even more perplexing, when I check "Sync Apps", I received the common warning but no erasing happen immediately when I approve the erase-&-replace [1st point which contradicts your post]. As a matter of fact, iTunes was able to detect whatever apps were already on my iPod Touch and when I click "Sync" (bottom right-hand corner of iTunes), the apps which were physically on the Touch already didn't get erased and re-uploaded.

After "syncing the apps", I looked through the other tabs and discover "Sync Music", "Sync Movies", "Sync TV Shows", "Sync Photos", "Sync Info" were are still unchecked [another point which differs from your norm, i.e. my apps library is treated/synced separately from my other media libraries]. In fact, I checked "Sync Music" next and got the warning again, & once again, the erasing didn't start immediately after I "approved" the warning. And even after syncing music, the checkboxes on "Sync Podcasts", "Sync Info", "Sync Photos" were once again, STILL unchecked. As if iTunes is waiting is for me to approve an overwrite of each library individually.

N.B. I did explicitly verified and observed that the podcasts and photos from the previously-"paired" library that was already on the iPod didn't get wiped by me syncing music & syncing apps from the new library.

This is the reason why I asked if iTunes treat each content type library with its own set of syncing "permissions". To summarize:

1. Actual erasing didn't commence immediately when I check the checkboxes of each "Sync ..." near the top of each content type tab and "approved" the all-the-familiar warning message. In fact, the erasing only begins when I click the "Sync" button near the bottom-right of iTunes.

2. Each content type/media type library are sync-ed (& replaced) separately, ignoring the approvals-to-replace given to other media library.

Are the 2 observations deemed "normal"? If so, what could I have configured that causes the new iTunes library to behave with the old iPod Touch in this exact manner?

Thanks for your clarification.

[jhollington]

When adjusting sync settings in iTunes, the "Sync" button in the bottom-right corner should change to read "Apply" and a "Cancel" button ("Revert" in iTunes 10) should appear above it. Nothing actually changes until you use the "Apply" button to apply those sync settings. iTunes 10 adds the feature where your capacity bar updates in real-time as you make changes to your sync settings, but that's only an estimate to help you adjust your settings. This is the case regardless of whether you're simply adjusting settings for your existing library or trying to sync to a new library. In fact, you can use the new "live" capacity bar in iTunes 10 to see exactly what's going to happen to your content.

Keep in mind as well that when automatically syncing to a new iTunes library, iTunes won't necessarily replace anything that is on your iPod but is still in your iTunes library. This definitely applies to Apps (as you've experienced), but also applies to music and other content, provided iTunes can recognize the content in your library as being the same as the content on your iPod. This generally only happens with media content if it is either purchased from the iTunes Store (in which case it has a catalog ID that iTunes can use), or if you've synced that library to your iPod before (as may happen when switching from manual mode back to automatic).

Essentially, iTunes does a quick inventory and comparison of what is in your library and what is on your iPod, and to save time leaves anything alone that already matches up.

All media content except for photos is treated as a single library. Other data such as apps, photos and contact/calendar info are special cases and are handled separately to some degree. You also cannot ever manually sync these content types -- it's automatic or nothing at all.

Your media content is all handled together as essentially one library (again, except for photos). When you connect your iPod to a new computer, these boxes are unchecked just to emphasize that nothing is being synced to your iPod from that computer. If you enable the "manually manage" option you'll see the same effect -- all of sync checkboxes on the Music, Movies, TV Shows, and Books tabs will be de-selected, and attempting to re-select ANY of them will essentially turn off manual mode -- you will even see the same warning as you do when trying to turn on these options from a different iTunes library. The warning appears for each tab just to make sure you're entirely sure about what you're about to do, but it should not be assumed that just because you see it for each checkbox that it only applies to the content on that particular screen. Most of the warning dialog boxes make it pretty clear that you'll lose all content, not just the content in that category, although not all of these are accurate (for instance, the one for "Music" says "songs and playlists" and none of them mention books, even though that forms part of it as well). The bottom line is that these warnings can be misleading. In some cases, they may not even appear at all when clicking the "Sync" checkboxes on a new computer.

Regardless, however, when you click the "Apply" button, you still get the standard "Erase and Sync" warning dialog.

Consider that disabling any of the "Sync" checkboxes even in your primary iTunes library actually removes the selected content from the iPod -- it doesn't just leave it on there and disable syncing of new content. The only exception to this is Photos -- you can uncheck Sync photos and will be provided with an option to remove your photos or leave them on your device as a static photo library.

Apps, Photos and Info (Contacts, Calendars and Bookmarks) are special cases. Since they normally contain your own personal data, iTunes will err on the side of caution, and syncing must be enabled separately from the media content sync options. If you set up your iPod on a new iTunes library and choose to not enable the syncing for these categories, this data will be left alone, even if you otherwise choose to overwrite your media content. Podcasts and iTunes U also work in the same manner if you are syncing them from the appropriate tabs.

In fact, until you choose to enable syncing for this content on the new computer, it will continue to be associated and sync with the old computer, even if you replace your media content or switch to manual mode. This means that you can even choose to sync your apps, photos, media content, podcasts and contact/calendar/bookmark info from separate computers from your main media library -- useful for scenarios where you may want to sync your device to a work computer for your calendar/contacts but still sync (or manually manage) your media content at home.

[ralliart122010]

1st of all jhollington, thanks for the comprehensive response. I really appreciate you taking the effort to clarify this

Originally Posted by jhollington

When adjusting sync settings in iTunes, the "Sync" button in the bottom-right corner should change to read "Apply" and a "Cancel" button ("Revert" in iTunes 10) should appear above it. Nothing actually changes until you use the "Apply" button to apply those sync settings...This is the case regardless of whether you're simply adjusting settings for your existing library or trying to sync to a new library...

I see; but what about when I'm not adjusting sync settings, i.e. when I hit a message like this:



What happens the moment I "approve" it? Does erase happens immediately, or iTunes will wait for me to piece together the new list of content I want to be placed on the iPod? (Because notice in this case, there ain't an "Apply" button, per se)

Originally Posted by jhollington

...Keep in mind as well that when automatically syncing to a new iTunes library, iTunes won't necessarily replace anything that is on your iPod but is still in your iTunes library. This definitely applies to Apps (as you've experienced), but also applies to music and other content, provided iTunes can recognize the content in your library as being the same as the content on your iPod. This generally only happens with media content if it is either purchased from the iTunes Store (in which case it has a catalog ID that iTunes can use), or if you've synced that library to your iPod before (as may happen when switching from manual mode back to automatic).

Essentially, iTunes does a quick inventory and comparison of what is in your library and what is on your iPod, and to save time leaves anything alone that already matches up...

I see and I concur. Hence a song that exists with the same tags in both my old and new library will not get wiped off when syncing to my new library. Same goes for videos and podcasts. And hence the "Erase and Sync" message is not a total wipe but rather detects (& leaves) what's already-there that's supposed to be there, remove what's already-there, that's not supposed to be there & top up with content that's supposed to be there, but currently not there (on the iPod)?

Am I accurate to paraphrase this way?

Originally Posted by jhollington

...All media content except for photos is treated as a single library. Other data such as apps, photos and contact/calendar info are special cases and are handled separately to some degree...

Can u elaborate on the part in brown? Because I am confused if the erase and sync will wipe those "type" of content (apps, photos, PIM) when one is simply choosing to sync music with the new library (hence adjusting the music syncing settings).

On the other hand, say I am adjusting the sync settings for the Music tab and I encounter the "Erase and sync" message, if I approve it, will the existing TV shows, Movies, and Podcasts on my iPod be erased subsequently if they were not detected in the new iTunes library?

Originally Posted by jhollington

...When you connect your iPod to a new computer, these boxes are unchecked just to emphasize that nothing is being synced to your iPod from that computer...

But if "Prevent...from syncing automatically" is UNchecked under the iTunes Preferences > Devices tab, a sync will try to commence when I plug a foreign iPod to an entirely new iTunes library right?

Originally Posted by jhollington

...The warning appears for each tab just to make sure you're entirely sure about what you're about to do, but it should not be assumed that just because you see it for each checkbox that it only applies to the content on that particular screen. Most of the warning dialog boxes make it pretty clear that you'll lose all content, not just the content in that category, although not all of these are accurate (for instance, the one for "Music" says "songs and playlists" and none of them mention books, even though that forms part of it as well). The bottom line is that these warnings can be misleading...

This is the exact kind of explanation that I was looking for. You have hit the nail on its head.

Originally Posted by jhollington

...Consider that disabling any of the "Sync" checkboxes even in your primary iTunes library actually removes the selected content from the iPod -- it doesn't just leave it on there and disable syncing of new content. The only exception to this is Photos -- you can uncheck Sync photos and will be provided with an option to remove your photos or leave them on your device as a static photo library.

Apps, Photos and Info (Contacts, Calendars and Bookmarks) are special cases. Since they normally contain your own personal data, iTunes will err on the side of caution, and syncing must be enabled separately from the media content sync options...

I tink it is because Apple wants iTunes to behave in a way to prevent one guy (& his/her iPod) going all over the place to accumulate songs and movies/TV shows that he may not have paid for. Hence the reason why only songs and videos are explicitly wiped.

Originally Posted by jhollington

...If you set up your iPod on a new iTunes library and choose to not enable the syncing for these categories, this data will be left alone, even if you otherwise choose to overwrite your media content. Podcasts and iTunes U also work in the same manner if you are syncing them from the appropriate tabs..

Do u means Podcasts will be left alone or wiped?

Originally Posted by jhollington

...In fact, until you choose to enable syncing for this content on the new computer, it will continue to be associated and sync with the old computer, even if you replace your media content or switch to manual mode. This means that you can even choose to sync your apps, photos, media content, podcasts and contact/calendar/bookmark info from separate computers from your main media library -- useful for scenarios where you may want to sync your device to a work computer for your calendar/contacts but still sync (or manually manage) your media content at home.

That is the appropriate design, i.e. imagine I just wish to plug my iPod into my colleague's laptop to charge and I accidentally wiped the songs, etc off my iPod simply because iTunes glazed me over with a few, misleading warning messages.

Btw, in other words, songs (less podcasts) + all videos = one library; everything else = their individual libraries?

Meaning all the following syncing combi with 2 computers, A & B are possible?

Scenario 1
A: sync songs + videos, contacts, bookmarks
B: sync calendar, photos, podcasts

Scenario 2
A: sync songs + videos, photos, bookmarks, podcasts
B: sync calendar and contacts

Scenario 3
A: sync songs + videos, calendar
B: sync contacts, photos, bookmarks, podcasts

[jhollington]

Originally Posted by ralliart122010

I see; but what about when I'm not adjusting sync settings, i.e. when I hit a message like this:



What happens the moment I "approve" it? Does erase happens immediately, or iTunes will wait for me to piece together the new list of content I want to be placed on the iPod? (Because notice in this case, there ain't an "Apply" button, per se)

As a rule of thumb, if you see the Erase and Sync message, it takes effect immediately. This prompt appears only when starting an actual sync operation, either because you have iTunes or your iPod set to automatically sync when you connect it or you've actually clicked the "Sync" or "Apply" buttons to initiate a sync.

Automatic sync for an iPod can be disabled in one of three ways:

1. Selecting Prevent iPods, iPhones and iPads from syncing automatically in the iTunes Preferences on the Devices tab. This globally disables automatic synchronization upon connection for any iPod you plug in.

2. Unchecking the Open iTunes when this (iPod/iPhone/iPad) is Connected on the "Summary" tab for that device in iTunes. This setting travels with the device and will prevent it from trying to sync automatically on any other computer you connect it to.

3. Holding down the CMD+OPT keys (Mac) or SHIFT+CTRL keys (Windows) while connecting your iPod, iPhone or iPad. This will prevent the automatic sync from running for that one connection. This is the "legacy" method that has been around since iTunes 4.0 -- the other two options above were only added in later versions, with the "Prevent" checkbox (#1) not showing up until iTunes 9.

This of course shouldn't be confused for "automatically" syncing your content versus managing it manually. An iPod that doesn't run the automatic sync will still be "set" to sync your content if you hit the "Sync" button unless you specifically switch it to manual mode on the 'Summary' tab for that iPod.

In the scenario where you're connecting an iPod to a brand new iTunes library and you haven't disabled the auto-sync (or you click the "Sync" button yourself) and then choose the "Erase and Sync" option, iTunes will basically treat the iPod as a brand new iPod in terms of media content (music, movies, TV shows, books) that is set to sync everything and will immediately try to do so. If there isn't enough space on your device, you'll get a message like the following and have to go back and adjust your selected content:

If you still have photo content on your device, iTunes will first offer to delete that content to make room instead.

If you choose not to remove the photos, iTunes leaves them alone (as described earlier) and tries to fit your content into whatever remaining space is available.

I see and I concur. Hence a song that exists with the same tags in both my old and new library will not get wiped off when syncing to my new library. Same goes for videos and podcasts. And hence the "Erase and Sync" message is not a total wipe but rather detects (& leaves) what's already-there that's supposed to be there, remove what's already-there, that's not supposed to be there & top up with content that's supposed to be there, but currently not there (on the iPod)?

That's exactly it.

The warning uses the language "Erase and Sync" as that is the perception of the average user. The fact that existing content is left alone is really just to save time, since the principle remains generally the same -- all content on your iPod is replaced with content from the current iTunes library. Following the new sync, your iPod will be either a complete mirror or a mirrored subset of the media content in the new iTunes library.

The way to look at it is thus: iTunes is conceptually the "master" library and the iPod/iPhone/iPad are extensions of that library.

The distinction between erasing and reloading and leaving existing content alone is really only relevant for applications, in the sense that your app data is not erased since the apps are left in place. Even if the device were completely erased and the apps were loaded on "fresh" however, you could still restore your backup that iTunes maintains for all iOS devices.

Can u elaborate on the part in brown? Because I am confused if the erase and sync will wipe those "type" of content (apps, photos, PIM) when one is simply choosing to sync music with the new library (hence adjusting the music syncing settings).

No, "Erase and Sync" will not automatically wipe that type of content by default. There are situations where iTunes may offer to delete content to free up space for your media content (as with Photos, and in fact during a full erase-and-sync as part of an automatic sync may provide a second prompt offering to replace the photos. In any case you always retain the right to say no.

Apps, Photos and PIM data will only be removed during an automatic sync if you specifically choose to enable sync on those tabs, or respond to a separate warning dialog that offers to erase/replace them for you to make space (I've never seen this happen with apps in recent iTunes versions, although it did come up occasionally back in iTunes 8).

You can essentially set up your iPod to sync everything on one computer and then connect to another one and when you choose the default Erase and Sync option, your Music, Movies, TV Shows, and Books settings will be reset and replaced with content from the new library. You'll find that the settings for Apps, Podcasts, Photos and Info are left alone (unchecked) on the new computer, and that data will remain in place unless you specifically enable those options separately (and acknowledge the warning dialog box, and hit the "Apply" button afterward). Further, if you leave those options alone in the new library and reconnect to your original iTunes library, you'll find that they're still set there and that content still syncs with the old library.

Note that in this scenario you'll still get an "Erase and Sync" warning message when you connect back to the original computer. Clicking the "Cancel" button will bypass this message and then proceed to sync whatever other information is still selected (ie, apps, contacts, podcasts, etc). You can also click the "Do Not Show Again" button to disable the warning for that specific iPod on that specific computer, so that you don't have to deal with it all the time if you're regularly syncing different info with two computers

On the other hand, say I am adjusting the sync settings for the Music tab and I encounter the "Erase and sync" message, if I approve it, will the existing TV shows, Movies, and Podcasts on my iPod be erased subsequently if they were not detected in the new iTunes library?

Yes for TV Shows, Movies and Books (both e-books and audiobooks). No for Podcasts (and iTunes U content also, which is basically just a special category of podcasts).

I find the behaviour with regard to e-books to be odd as they're a very different type of content, but my guess is that they just inherited the behaviour for audiobooks, which are really just another type of audio content, and in fact until very recently (iTunes 9.1) were managed from the "Music" tab.

But if "Prevent...from syncing automatically" is UNchecked under the iTunes Preferences > Devices tab, a sync will try to commence when I plug a foreign iPod to an entirely new iTunes library right?

Correct. This is the same as connecting the iPod with this option checked and then hitting the "Sync" button manually without changing anything.

The phrase "automatic sync" is a bit of a misnomer, since people use it to refer to the opposite of managing music manually, however it is not necessarily "automatic" in that sense that it runs unattended, since you can disable that aspect of it and simply hit the "sync" button instead to sync on demand.

I tink it is because Apple wants iTunes to behave in a way to prevent one guy (& his/her iPod) going all over the place to accumulate songs and movies/TV shows that he may not have paid for. Hence the reason why only songs and videos are explicitly wiped.

That's actually not entirely true, although many have speculated that this is the case.

Firstly, you can set an iPod to "manual" and simply drag and drop content onto it from as many computers as you like. A five-account limit per iPod does exist to prevent the scenario you describe with regard to content purchased from the iTunes Store (ie, you can sync to 50 computers if you want to, but the iPod can only contain content purchased with up to five iTunes Store accounts, regardless of which computers it comes from), however iTunes and the iPod won't police any content that is not purchased from the iTunes Store.

Further, the restrictions on transferring content from the iPod back to your computer were almost certainly born from a desire to prevent piracy by allowing people to share their iPod content too easily with their friends. The feature to Transfer Purchases wasn't added until a couple of years ago, and provided an authenticated way to ensure that you were only transferring your own content, and since the computer you're transferring to must be authorized for the same iTunes Store account as the content on the device, you would be limited to a maximum of five computers that you could transfer content back to.

IMHO, the real reason that the sync method works in the way it does is to keep things simple, at least at its roots (remember this was designed back when music was the only content to be concerned with). While people who are used to different systems may be confused with the fact that they can't plug into more than one library, the opposite approach would be potentially much more confusing -- how do you manage content that comes from multiple libraries? Which library takes precedence in the case of duplicate content, or in the case that there's not enough room on the iPod? Where do playlists come from? How are duplicate playlists handled? Where do ratings and play counts go to and where do they come from? None of these are insurmountable, but they'd all be far more confusing than just taking the approach that if you want to sync, you do so with one library, and if you want to transfer content from multiple libraries, you go to manual mode.

In short, in sync mode the iPod is treated as an extension of the iTunes library. In manual mode it's treated as its own, distinct media library.

Note that manual mode only applies to the core media library (music/movies/TV shows/books). Apps, Podcasts, Photos and PIM info can only be synced, and therefore only associated with a single computer (but not necessarily the same one for each type).

Do u means Podcasts will be left alone or wiped?

Podcasts are left alone, provided they were transferred from the settings on the "Podcasts" screen. Podcasts can also be transferred manually or as part of playlists that are selected on the Music screen, in which case they will be treated as any other music track and wiped.

In fact, like apps, photos and PIM info, you can still sync your podcasts with a different computer.

That is the appropriate design, i.e. imagine I just wish to plug my iPod into my colleague's laptop to charge and I accidentally wiped the songs, etc off my iPod simply because iTunes glazed me over with a few, misleading warning messages.

You should always be prompted with an "Erase and Sync" dialog box before doing anything that would remove content, which is pretty clear. Even the other warning messages that you see when selecting specific content types are preliminary to the final "Erase and Sync" dialog box, which appears as a final warning once you click the "Apply" button to save those settings and begin syncing.

The only time you won't see an "Erase and Sync" dialog box is when you're syncing to the same iTunes library. This obviously makes sense, but can be a concern if you're in a situation where you've deleted a bunch of stuff from your iTunes library entirely but don't want it deleted from the device. In this case you would need to disable automatic sync (by enabling the "Prevent..." option described above), and then either switch your iPod to manual mode or use a third-party tool to recover the lost information and import it back into your iTunes library. Note that if you're dealing with purchased content that has been removed from your iTunes library, then iTunes will notify you of this and give you an opportunity to transfer these items back:

Transfer purchases applies to all content purchased or downloaded from the iTunes Store including music, movies, TV shows, apps, audiobooks and e-books. It does not apply to podcasts and iTunes U content as these don't really come from the iTunes Store (iTunes merely provides the directory and download links).

Note that iTunes will only remove items from your iPod if they are no longer listed in the iTunes library. It doesn't care whether the actual file can be found or not.

Btw, in other words, songs (less podcasts) + all videos = one library; everything else = their individual libraries?

If you want to look at them as "libraries" then yes. It's broken down like this:

- Music, Movies, TV Shows, Books, Ringtones (sync, manual, or none)
- Apps (sync or none)
- Podcasts / iTunes U (sync, manual, or none)
- Photos (sync or none, can disable sync and leave on device)
- Info -- Contacts, Calendars, Bookmarks, Notes (sync or none, can disable sync and leave on device)

Enabling manual mode automatically de-selects synchronization for Music, Movies, TV Shows, Books and Ringtones. Sync settings remain enabled for other types of content.

The manual mode setting is applied to the iPod or iPad and will remain enabled on any computer you connect your device to. Manual mode for the iPhone can only be enabled on a single computer, possibly due to licensing issues with ringtones (the iTunes Store Terms state that ringtones may only be synced/transferred from a single computer, and enabling manual mode could potentially bypass this).

Like photos, when deselecting Info items for synchronization you're given the opportunity to leave the info on the device or remove it.

Also, when enabling the sync for Info items on a new computer, any existing items on the iPod, iPhone or iPad can be either replaced or merged with your existing info:

Meaning all the following syncing combi with 2 computers, A & B are possible?

Not quite. All Info items must be synced with the same computer -- you can't get your contacts from one and your calendar from another. Of course, with iOS devices there are other wireless methods to sync your calendar/contact info, in which case iTunes is not involved at all in the process. However, if you're syncing via iTunes, all "Info" items must come from the same iTunes source.

[ralliart122010]

@jhollington, I cannot thank you enough, for your response truly dug into the nook & crannies of the multitude of use cases one may encounter with iTunes syncing.

I did a revamp of my library recently & wrote about my observations in a blog entry. Wanted to give some inferences about syncing behaviour but didn't wanna mislead any potential readers with a less-than-accurate understanding of what's really going on (with iTunes). & you (as well as ScoobZ) have helped me greatly in this endeavour.

[ScoobZ]

Agreed. Hats off to jhollington for the info in this thread! I learned a ton.