From Retro CDN
The revision history (also called page history and edit history) of all pages is available to anyone at any time. The history consists of the complete content of all old versions of the article, plus a record of the date and time of the edit, the user who made the edit, the edit summary, and the possible marking of a minor edit.
(One exception is for pages that have been deleted — the only record available for non-administrators is the deletion log. Once a page is deleted, the edits to that page are not recorded anywhere, including the user contributions page. Only administrators may check the revision history of deleted articles and undelete them.)
Every page has a link titled "History" (or "Page history" in the older skin), from which the list of edits for that article may be viewed. The recent changes and related changes pages also have links to the histories of listed pages.
Every line in a page history represents one edit to the given page and the version resulting from it. From the history page, you can compare any two versions of the page:
- The cur links compare the selected version with the current version of the page.
- The last links compare the selected version with the immediately preceding version of the page.
- You can also use the radio buttons to compare any two versions of the page.
If a page has been renamed in the past, the page's entire version history is moved as well, but the move itself is not shown. The move itself is shown in the edit history of the page with the old title, which is automatically made into a redirect page.
An image (or any uploaded file) can be replaced (but not edited directly) by a different image, by uploading a new image file with the same name. Again, all versions of a file are kept. The image history list appears as part of the image description page, which appears when you click on an image. The history consists of the current and old versions of the image.
The history of the descriptive text for the image is also recorded, in a manner similar to that of the textual pages themselves.
Revision history for articles containing images or templates
Articles may contain images or templates that transclude content from another part of the database into an article. In effect, the transcluded content is not part of the article source text itself, although it is displayed as part of the article. The revision history does not show changes to transcluded content (either images or templates); any such changes are listed on the individual image or template page histories.
Old versions of articles do not show corresponding old versions of images or templates, but rather the latest version, unless the file names of the images or templates have been changed.
For talk pages and other similar pages, it is considered better to archive content rather than save it only in the page history. This is because old versions of articles are not indexed either by Google or by the local search utility. Page histories can only be searched after using the export utility.
In addition, archived pages can be organized and titled in a user-determined fashion that is simpler to navigate and can be better labeled using edit summaries.