May 16, 2014, 10:24 AM — Deleted files can often be recovered, and that's a problem when you're passing your PC or PC-related tech along to someone else. Whether it's sensitive financial data, business documents, or scandalous photos that could be used to blackmail you, you probably don't want people getting their hands on your private stuff.
Fortunately, you can take steps to protect your data, whether you're getting rid of a PC, external hard drive, or USB stick. Here's how! (And here's how to wipe mobile devices clean.)
Mechanical hard drives vs. internal solid-state drives vs. external drives
Deleted files can be recovered from some types of drives, but not others. Here's a quick summary of how different drives handle deleted files.
Mechanical hard drives: Old-school mechanical hard drives--the kind with a spinning magnetic platter--are still used in PCs. If your PC doesn't have an SSD, it has a mechanical hard drive. Files you delete from these drives can be recovered. When you delete a file from such a drive, the drive just marks the file's data as deleted. Until it's overwritten in the future, people can scan the drive and recover the marked-as-deleted data.
Internal solid-state drives: Solid-state drives use a feature called TRIM. When you delete a file from a solid-state drive, the operating system informs the drive that the file was deleted. The drive then erases the file's data from its memory cells. This is done to speed things up--it's faster to write to empty cells--but it has the benefit of ensuring files you delete from internal SSDs can't be recovered.
External solid-state drives and other removable media: TRIM is used only for internal SSDs. In other words, if you have an external SSD in an enclosure and you connect it to your computer via USB, TRIM won't erase files you delete. This means deleted files can be recovered from that external SSD. Deleted files can also be recovered from USB flash drives, SD cards, and other types of removable media.
If you have a PC with a solid-state drive, you just need to reinstall your operating system to erase your data. If you have a PC with a mechanical drive, you'll need to ensure your drive is wiped before reinstalling your OS. If you have an external drive, you'll need to wipe that, too.