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For example, at Microsoft we redirect the "Documents" folder (previously known as "My Documents" in Windows XP) to a share on the server (of course, we use access controls on the folders to make sure that I am the only person who can see my files).

By redirecting key folders like the Documents folder to a file share, my documents are available to me no matter which one of my Windows PCs I am using. The problem of course is what happens when I don't have access to the server -- such as when I am not on the corporate network or perhaps sitting on an airplane. Frankly, the same problem exists with any file share that I might try to access when I am not on the corporate network.

Well, as it turns out, we have had a very cool feature in Windows (actually, it's been there since Windows 2000) called "Offline Files." (We actually used to call it "Offline Folders.") As the name implies, Offline Files allows you to mark particular folders (and their sub-folders) to be available offline. When you are on the network, Offline Files automatically synchronizes the folders so that you have a copy of them locally on your hard disk. Then when you are offline (and don't have access to the actual server), Offline Files makes it look like you are online by simply accessing the locally cached copy. Later, when you do have access to the file share, Offline Files automatically synchronizes any changes you have made offline with the online version and vice-versa.



So why am I telling you about a feature that's been available since Windows 2000 here in the Windows Vista Team blog? Well, frankly, because we have made quite a few enhancements in the Offline Files support for Windows Vista. Here are some examples.

In Windows XP, the transition from online to offline was pretty seamless -- which was good. The problem was that when you came back to the network and tried to reconnect, it was sometimes less than seamless -- and we fixed that with Windows Vista. Now, when Windows Vista detects that the server is available, not only do we automatically synchronize any files and folders that changed, but we also automatically redirect any open files to the online copy.

Another thing that always bugged me before Windows Vista was the fact that there was no way to force the transition to "offline mode." I don't know about you, but before I get on a plane for 5 hours I want to make sure that all the documents that I need are locally available on my laptop. Prior to Windows Vista, I had to manually turn off my wireless card to make the system think I was offline. The problem there was that it was a complete disconnect that killed my connection to the Exchange Server. Now, with Windows Vista, there is a button right in the Explorer tool bar (that is available whenever I am looking at a file share) called "Work Offline" that automatically forces the transition to offline mode. Of course, when you click the button it changes from "Work Offline" to "Work Online" so that you can force the transition back. This is a simple way to verify exactly what you will see when you are travelling to double-check that you have everything that you need.



We did some other "fit-and-finish" things to Offline Folders to make it more usable as well. One example of this is the way that we synchronize the offline files with the online copy. Offline Files in Windows Vista keeps track of the blocks that are modified while offline and only transfers the changed blocks to the server. This makes synchronization of changes from the client to the server much faster. I should note that this optimization is only used when transferring changes from client to server; it is not used when transferring changes from the server to the client. I should also note that some applications (like Microsoft Word) create a new file when you modify an existing document, so you won't see the benefit here.

We also changed the synchronization approach so that we now only try to synchronize the shares for the user that is logged on. This addresses a problem that users would hit in the past when we used to try to sync all offline folders and the user saw an "access denied" error for the folders that actually belonged to someone else. Navjot Virk, the program manager for Offline Files, wrote a great blog entry on Offline Files that covers this in more detail and I encourage you to check it out.

There are many ways you can turn on Offline Files. The simplest way is to browse to a file server, right-mouse to get the context menu for the folder or file that you want to be automatically cached, and select "Always Available Offline." You are done; it's just that easy. Work with the files/folders just like you would normally whether you are travelling (and disconnected from the network) or working at your desk (and connected to the network). Windows Vista's Offline Files automatically synchronizes all the changes for you without you having to do anything.