applied and a 0 state (no current flow) when the CG voltage is applied. After being written to, the insulator traps electrons on the FG, locking it into the 0 state. However, in order to change that bit, the insulator has to be "overcharged" to erase any charge already stored in it. This requires higher voltage, about 10 volts, much more than a battery can provide. Flash systems include a "charge pump" that slowly builds up power and releases it at higher voltage. This process is not only slow, but degrades the insulators. For this reason flash has a limited number of writes before the device will no longer operate effectively. NRAM reads and writes are both "low energy" in comparison to flash (or DRAM for that matter due to "refresh"), meaning NRAM could have longer battery life. It may also be much faster to write than either, meaning it may be used to replace both. Modern phones include flash memory for storing phone numbers, DRAM for higher performance working memory because flash is too slow, and some SRAM for even higher performance. Some NRAM could be placed on the CPU to act as the CPU cache, and more in other chips replacing both the DRAM and flash. NRAM is one of a variety of new memory systems, many of which claim to be "universal" in the same fashion as NRAM – replacing everything from flash to DRAM to SRAM. An alternative memory ready for use is ferroelectric RAM (FRAM or FeRAM). FeRAM adds a small amount of a ferro-electric material to a DRAM cell. The state of the field in the material encodes the bit in a non-destructive format. FeRAM has advantages of NRAM, although the smallest possible cell size is much larger than for NRAM. FeRAM is used in applications where the limited number of writes of flash is an issue. FeRAM read operations are destructive, requiring a restoring write operation afterwards. Other more speculative memory systems include magnetoresistive random-access memory (MRAM) and phase-change memory (PRAM). MRAM is based on a grid of magnetic tunnel junctions. MRAM's reads the memory using the tunnel magnetoresistance effect, allowing it to read the memory both non-destructively and with very little power. Early MRAM used field induced writing, reached a limit in terms of size, which kept it much larger than flash devices. However, new MRAM techniques might overcome the size limitation