Why Deleted Files Aren’t Erased Immediately
If you’re wondering why your computer doesn’t just erase files when you delete them, it’s actually pretty simple. Deleting a file’s pointer and marking its space as available is an extremely fast operation. In contrast, actually erasing a file by overwriting its data takes significantly longer. For example, if you’re deleting a 10 GB file, that would be near-instantaneous. To actually erase the file’s contents, it may take several minutes – just as long as if you were writing 10 gigabytes of data to your hard drive.
To increase performance and save time, Windows and other operating systems don’t erase a file’s contents when it’s deleted. If you want to erase a file’s contents when it’s deleted, you can use a “file-shredding” tool – see the last section for more information.
Solid-State Drives Work Differently: None of this applies to solid state drives (SSDs). When you use a TRIM-enabled SSD (all modern SSDs support TRIM), deleted files are removed immediately and can’t be recovered. Essentially, data can’t be overwritten onto flash cells – to write new data, the contents of the flash memory must first be erased. Your operating system erases files immediately to speed up write performance in the future – if it didn’t erase the file data immediately, the flash memory would first have to be erased before being written to in the future. This would make writing to an SSD slower over time.