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If you are experiencing issues downloading Mavericks from the Mac App Store, here is a helpful troubleshooting article.
If downloading an app is interrupted
Once an Internet connection is reestablished, your purchased downloads should automatically restart. The Mac App Store may alert you that there was an issue with the download and ask if you'd like to restart the download(s). Confirming will restart all pending downloads. For more information on this topic, see Mac App Store: How to resume interrupted downloads.
Note: The download time will vary according to the file's size and your Internet connection speed. Refer to this article about iTunes Store purchases for more information about download times for large files.