Ghosting in Windows SharePoint Services

Version 2

A page is considered Ghosted when it is built using the site template files on the file system. That site template is merged with personalization data from the database to display the final output. There are two reasons we like Ghosted pages:

1. They read from the file system, which is faster than the database.
2. They reference the site template, which means if you update your site template, you update all the sites referencing the site template - this was key to customizing the look and feel of your WSS deployments.

A page is considered unGhosted when it has been modified by a SharePoint compatible editor (read: FrontPage 2003) and can no longer be built using site template files. Behind the scenes, there is an entry in the Docs table for each file in your WSS site. As long as the Content field is NULL, the file is considered Ghosted. The moment you make a change using an editor, a snapshot of the file is saved into the database and your file is unGhosted.

Version 3

The concept of Ghosting still exists in WSS Version 3 but it is not as big of a problem as it used to be. In my experience, the issue most people are concerned with is the inability to centrally update the look and feel of their web site if their pages have been unGhosted. With the introduction of Master Pages, users will still be able to update a page's look and feel centrally, even if pages have been unGhosted. The SharePoint guys have also done some work to improve performance so the performance hit on unGhosted pages is smaller.