Asked by: Ron Clarke, Hereford
Flash storage devices are based on chip technology called Electronically Erasable Programmable Read Only Memory (EEPROM). USB flash sticks use a refined version of EEPROM. In its earliest incarnation, individual bits of data on the chip had to be erased separately. It was like a vertically stacked library where getting at one book at the bottom of a pile meant having to move the books above it one at a time.
But now multiple memory cells can be addressed simultaneously, allowing entire blocks to be written and rewritten in one go, like moving a pile of books, rather than one book, at a time. It requires considerable on-chip processing and is a feat that has come about through recent advances in chip design and miniaturisation, ushering in USB drives capable of storing gigabytes of data.