A customer reported an issue with the title “The notification balloon for Low Disk Space does not appear even if the free disk is very low.” They provided the following steps:

• Install Windows 7 64-bit on a SATA drive.
• Copy files to the system drive until disk space becomes low.
• Observe that the notification balloon for Low Disk Space does not immediately appear.
• The balloon appears approximately ten minutes later.

You read through the steps nodding, “uh huh, uh huh”, and then you get to the last step and you say, “Wait a second, the subject of your report was that the balloon doesn’t appear at all, and now you’re saying that it appears after ten minutes. So it does appear after all. What is the problem?” The customer explained that on earlier versions of Windows, the Low Disk Space warning balloon appeared within one minute, whereas in Windows 7 it can take up to ten minutes for the balloon to appear. Yup, that’s right. In previous versions of Windows, Explorer checked for low disk space once a minute. The Windows performance folks requested that the shell reduce the frequency of checks to improve overall system performance, and the shell team agreed to reduce the frequency to once every ten minutes. (The performance team made other suggestions to reduce the impact of that code that runs every ten minutes.) So yes, in Windows 7, it may take up to ten minutes for Explorer to report that you are low on disk space. But Explorer never promised that those reports would be timely. Or that they would even appear in the first place. The behavior is not contractual; it’s just a courtesy notification.

Related: How full does a hard drive have to get before Explorer will start getting concerned? and How do I disable the low disk space notifications?