GoKawiilMost high-capacity flash storage is NAND, in which memory cells store electrical charge in an insulated storage layer, and the various voltage states are interpreted as data.
Modern NAND squeezes considerably more out of that basic idea. 3D NAND stacks cells vertically rather than arranging them only across a flat plane, and TLC and QLC designs store three or four bits per cell. Both pack more storage into roughly the same space and reduce the cost per gigabyte.
Those gains made flash particularly well suited to portable electronics. Unlike a hard drive, an SSD doesn't have a spinning platter or mechanical read head, so it offers lower access latency, handles bumps better and fits ever-thinner devices. If you've upgraded an old PC to an SSD, you may remember the first boot afterward. All of a sudden, the computer doesn't require a motivational speech before opening Chrome.
That still doesn't make flash a replacement for RAM. System RAM is much faster and handles temporary working data, while NAND provides persistent storage. The term flash ROM is also misleading, as flash can be erased and rewritten.