Unallocated space doesn't have filesystem entries, hence, no file change, access, or modification times.
Worse: many filesystems don't note creation time but change time. I'd have to check what the status is for NTFS (the most likely consumer FS), but that's the case for virtually all Unix-and-similar filesystems: ext3/4, HFS, etc.
The BSDs, Windows, OS X, and Mac OS classic and their corresponding filesystems all supported this for decades. Linux is the only major holdout, because according to Linus, "it's all totally useless and people can't even agree on a name." [1]
Thanks for that. I know that the inode structure doesn't, or at least didn't return this, for a long time (occupational hazard: outliving your education's "best used by" date). Which was why I'd already edited the initial "most" to "many" describing filesystems above (prior to posting).
I'll still maintain it's not universally available on filesystems. And is unreliable (many allow changing this value, see, e.g., touch(1)). And that unallocated space lacks filesystem metadata.
Worse: many filesystems don't note creation time but change time. I'd have to check what the status is for NTFS (the most likely consumer FS), but that's the case for virtually all Unix-and-similar filesystems: ext3/4, HFS, etc.