Files on magnetic hard drives remain on the drive even after they are deleted, so they can be recovered later with forensic tools. Sometimes SSDs work the same way, but under other conditions they erase this latent data in a "garbage collection" process. Understanding when and how this happens is important to forensic investigators and people who handle confidential data.
I'll explain the purpose of garbage collection, and how it is affected by the operating system, SSD model, BIOS settings, TRIM, and drive format. I'll demonstrate SSD data evaporation on a MacBook Air and a Windows system, using my "evap" tool (available for everyone to use) that makes it easy to test SSDs for data evaporation.