Williams is also recognised for his invention of the Williams tube, an early memory device. A PLD is a combination of a logic device and a memory device. Writing to a flash memory device takes longer than reading from it. The typical phase-change memory device design is shown. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. This means data can be transferred from one memory device to another memory device. For these reasons, doodling is used as an effective study tool and memory device. In May 2012, JEDEC published the JESD209-3 Low Power Memory Device Standard. Williams tubes were the first true random-access memory device. A racetrack memory device is made up of many such wires and read/write elements. Drops have included offline copies of the Korean Wikipedia on a bootable USB memory device. Unlike other acting techniques, this step is NOT a memory device. On 25 August 2014, JEDEC published the JESD209-4 LPDDR4 Low Power Memory Device Standard. The term generally refers to a simple, tamper-proof, read-write memory device. A memory device is built from a grid of such "cells".