your hard drive has never deleted a file

Drag a file to the bin. Empty the bin. Now watch the drive. Nothing on it moves. The bytes sit in the same sectors they were in a second ago. What changed is one entry in a table, flipped from used to free, and the operating system no longer points at it. The bytes stay until the disk needs that exact spot for something else. That could be this afternoon. It could be never.

Databases don't even pretend. Most apps with a delete button have a column on the row called deleted_at. Press the button and the row gets a timestamp. Every query that shows the live data ends with a clause, where deleted_at is null, and the row drops out of view. It is still there for support, for analytics, for the lawyer. Engineers call this soft delete, and it is the default, because a hard delete is the kind of thing that gets someone paged at 3am.

In July 1996 Peter Gutmann, a researcher at the University of Auckland, presented a paper at the USENIX Security Symposium in San Jose with a recipe for erasing a hard drive for real: 35 passes, each one writing a specific pattern over the spot. It became a product feature. Wipe tools put "Gutmann" on a dropdown next to the Department of Defense standard, and people picked it because 35 sounded like the number that meant gone.

Gutmann later added an epilogue to his own paper. The 35 passes had been designed to cover every drive encoding at once; no single drive used more than a few of them. Running the whole set, he wrote, was pointless, and people had started treating it as a voodoo incantation. For a modern drive, "a few passes of random scrubbing is the best you can do."

Then drives stopped being magnetic. In 2011 four researchers at UC San Diego (Michael Wei, Laura Grupp, Frederick Spada and Steven Swanson) wrote a known pattern onto SSDs, ran every erase method they could find, and then took the drives apart and wired the flash chips to a board of their own so they could read the cells raw. Of twelve drives with a built-in secure erase command, four actually erased. One reported success with every byte still readable. For single-file overwrites, all 35 methods they tried failed; between 4 and 75 percent of each file was still on the chips. The cause is the controller. Flash wears out, so the drive spreads writes around and keeps the old copy wherever it was. Overwriting a file writes a new one next to it.

when memory is free, forgetting is a decision

In May 2013 a 24-year-old examiner named Richard Hickman at Decipher Forensics in Orem, Utah, told a local news station what happens to a Snapchat after its ten seconds. On Android, nothing. The photo lands in a folder called RECEIVED_IMAGE_SNAPS, and when the timer runs out the app appends .nomedia to the filename, which tells the gallery not to show it. Remove the extension and the picture opens. Decipher charged parents three to five hundred dollars per phone.

Anyone who had a PC in 1998 has watched this from the other side. Windows 98 defrag opened a map of tiny coloured blocks and spent an afternoon sliding them into rows. It felt like cleaning. It wasn't. Defrag deletes nothing; it gathers the pieces of each file and packs them closer together so the head doesn't have to travel. Same data, tighter. Vista took the map away, which is probably why nobody defrags anymore.

The human version shipped in Japan in the last days of 2010. Marie Kondo's method is a sanitize command for an apartment: hold each object, ask whether it sparks joy, and if not, thank it out loud for its service and let it go. Ten million copies. Cathy Hirano's English translation came out from Ten Speed Press in 2014, and the donation bins filled with things that had been thanked.

Vilhelm Hammershøi painted the apartment at Strandgade 30 in Copenhagen for eleven years, from 1898 to 1909, over and over. The same grey walls, the same doors, his wife Ida almost always seen from behind. He moved the furniture between versions and sometimes painted the mouldings out. In this one she holds a platter on her hip and faces the wall, and the tureen on the table is the only thing in the room with a pattern. The room was never emptied. It was repainted.

New apartment, Kondo'd top to bottom. Her mug got thanked and went in the bag. The mattress came along, because a mattress is a mattress, and it kept its dent.

Her side is the side by the window now.

Free space is space nobody has written to yet.

The painting: Vilhelm Hammershøi, Interior with Young Woman Seen from the Back (c. 1903–04), Randers Kunstmuseum. Public domain.

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