It all comes clear when you remember that despite the loose use of the term 'syncing', this isn't what iCloud is doing. All the data lives on the server and is read from there by the Macs and devices (there are locally cached copies to speed things up but you can ignore them for operational purposes). Think of it as being like webmail and it falls into place.
This does and yet doesn't make complete sense to me.
It sounds like it's best to go to iCloud and make changes there.
However, one day after switching to iCloud, changes to Apple Mail on any device are reflected on all the other devices, and a change to my Safari bookmarks, on my MacBook Air, has been reflected on my iMac, iPhone, and iPad too.
Please, I am not trying to be a nit picker here, just trying to better visualize/understand how this would not be considered syncing.
OK: you have two Macs, A and B.
Syncing: You add an item to A. When the syncing process takes place - which could be soon or later - the item is copied to the server. Then it is copied to B. If you turn off syncing the item will still be on both. On MobileMe the syncing process could take quite a long time.
Subscribing (which is what happens with iCloud): the data lives on the server. When you add an event on A you are actually adding it to the server. It is therefore immediately available to B which is reading the server. If you turn the process off (e.g. signing out if iCloud0the item will disappear from both Macs.
iCloud carries out local cacheing so that the reading process is kept fast and data is available while you are offline: but you should regard this as a background process and ignore it.
Thanks, it's clearer now.
The lesson I am taking away is don't sign out of iCloud.
On my computers Sys Prefs > iCloud has a Sign Out button.
However, checking out my iPhone and iPad, I see under Settings > iCloud, only Delete Account. I see no way to sign out from iCloud on a device running iOS 5.
Am I right?
Thanks once again,
Delete account is the same as 'Sign Out' on the Mac - you'd think they'd name them the same, wouldn't you - but they both do the same thing: disconnect you, so that you can't read the server, and flush the caches.
So if you sign out/delete, your data disappears from your Mac/device; but it re-appears when you sign in again.
I am replying to my own post over a year later because I found this in a long, technical article about developers complaining about how iCloud works: all caps are from me.
In concept, the service is pretty simple. A central iCloud server HOLDS THE TRUTH: the canonical version of the user's data for an app. As the user manipulates an app's data, iCloud tracks and reconciles the changes into the central truth, and makes sure that all copies of the data, on each computer, are brought up to date. In order for this to work, though, a lot has to happen behind the scenes. What we casually refer to as iCloud is many parts, each with a role to play.
So, it would _seem_ to be a wise policy to make any changes to iCal, Contacts, etc., after logging into your iCloud account. I continue to see odd behavior in both of these applications (i.e., duplicate entries in Contacts and Calendar reminders which fail to remind) when I make changes on my MacBook or iMac, but Mail seems changes seem to work just fine.
So, it would _seem_ to be a wise policy to make any changes to iCal, Contacts, etc., after logging into your iCloud account.
This would be the case anyway, since you should be logged in all the time in System Preferences>iCloud - if you log out your data will disappear from the device.
If you make an alteration while you are out of range of a network - in 'Airline mode' on an iPhone, for example - then the change is cached on the device and transmitted to iCloud when a connection is available.