A memristor is an electrical component that limits or regulates the flow of electrical current in a circuit and remembers the amount of charge that has previously flowed through it. Memristors are important because they are non-volatile, meaning that they retain memory without power.
The original concept for memristors, as conceived in 1971 by Professor Leon Chua at the University of California, Berkeley, was a nonlinear, passive two-terminal electrical component that linked electric charge and magnetic flux. Since then, the definition of memristor has been broadened to include any form of non-volatile memory that is based on resistance switching, which increases the flow of current in one direction and decreases the flow of current in the opposite direction.
A memristor is often compared to an imaginary pipe that carries water. When the water flows in one direction, the pipe's diameter expands and allows the water to flow faster -- but when the water flows in the opposite direction, the pipe's diameter contracts and slows the water's flow down. If the water is shut off, the pipe retains its diameter until the water is turned back on. To continue the analogy, when a memristor's power is shut off, the memristor retains its resistance value. This would mean that if power to a computer was cut off with a hard shut down, all the applications and documents that were open before the shut down would still be right there the screen when the computer was restarted.
Memristors, which are considered to be a sub-category of resistive RAM, are one of several storage technologies that have been predicted to replace flash memory. Scientists at HP Labs built the first working memristor in 2008 and since that time, researchers in many large IT companies have explored how memristors can be used to create smaller, faster, low-power computers that do not require data to be transferred between volatile and non-volatile memory. If the storage heirarchy could be flattened by replacing DRAM and hard drives with memristors, it would theoretically be possible to create analog computers capable of carrying out calculations on the same chips that store data.
R. Stanley Williams explains how a memristor works.