jj juice, if you give or sell me your old computer, with a formatted drive and re-installed OS, I can recover almost all your old data with any of the many giveaways we have seen here. Or with the free Recuva.

Formatted does NOT wipe the original data. It only 'tells' your computer it can overwrite all existing data.

little ricky, When files are deleted from your computer/disk formatted, you are simply deleting the directory listing for the particular file. Even thou it is no longer "visible", the data remains on the disk and isn't permanently removed until it's overwritten with new data. Just re-installing an OS only over writes the area previously used by the OS. Other data remains. The only real way to actually wipe a drive so nothing can be recovered is a complete overwrite of the complete drive, usually consisting of all zeros, except the 511th and 512th byte..those are left with the code that allows the BIOS of an MBR system to recognize the drive is ok to write to. Or take a hammer and nail to it and completely destroy the platters inside.
UEFI and GPT systems are a bit more difficult, but again, unless the complete drive is over written, old data that isn't part of the O/S could be recovered with advanced methods. I had an old drive here that I did a complete format on, but decided to check it

little ricky, you might de amazed.

Many formats, like .pdf and .doc have a characteristic header that can be found. And from there ...

I remember long, long ago I used to replace the two bytes in the header of an encrypted WordPerfect file to make unwanted de-encryption more difficult.

Bob,

It sometimes makes sense to run an app from a bootable USB drive, e.g. today's GOTD, DoYourData Super Eraser, but it seems like most often the app in question is not portable, often because of where it stores activation data. One potential solution is to create a Windows To Go USB drive, which is really just a copy of win10 plus the files needed for it to boot. You can create one using rufus & a win10 ISO -- Enterprise & I *think* Edu versions won't try to activate if that matters to you -- win10 will for the most part run fine unactivated. And since it's a regular copy of Windows, you can install & activate software like DoYourData Super Eraser.

rufus[.]ie/en_IE.html