SSD

In 2018, a second-hand study from a university in the United Kingdom made headlines after researchers purchased 200 used hard drives from eBay and other online marketplaces. Out of 200 drives, they found that 59% still contained recoverable data—including personal photographs, financial records, and in one case, a complete database of a company’s payroll system. The previous owners had formatted these drives. Some had even run “secure erase” tools. Yet the data remained. ...

When you save a file to a solid-state drive, something happens at the atomic level that your hard drive could never accomplish. Electrons tunnel through an insulating barrier and become trapped in a microscopic cage, where they can remain for years without power. This is the fundamental magic of flash memory—and understanding it explains everything from why SSDs slow down when full to why they eventually wear out. The first commercial flash memory chip appeared in 1988, but the technology traces back to a 1967 paper by Dawon Kahng and Simon Sze at Bell Labs. They proposed storing charge in a transistor’s floating gate—a conductive layer completely surrounded by insulator. Nearly six decades later, every NAND flash cell operates on this same principle, even as manufacturers have stacked cells hundreds of layers high and squeezed multiple bits into each one. ...