Read-write memory such as NVRAM can be used to store calibration constants, passwords, or setup information, and may be integrated into a microcontroller.
By applying higher power than normal, a selected diode can be burned out (like a fuse), thereby permanently setting that bit to 0.
Another drawback is the performance limitations preventing flash from matching the response times and, in some cases, the random addressability offered by traditional forms of RAM.
Those who required real RAM-like performance and non-volatility typically have had to use conventional RAM devices and a battery backup.
For example, IBM PC's and successors beginning with the IBM PC AT used nonvolatile BIOS memory, often called CMOS RAM or parameter RAM, and this was a common solution in other early microcomputer systems like the original Apple Macintosh, which used a small amount of memory powered by a battery for storing basic setup information like the selected boot volume.
Much larger battery-backed memories are still used today as caches for high-speed databases that require a performance level newer NVRAM devices have not yet managed to meet.
This process has the disadvantage of mechanically degrading the chip, however, so memory systems based on floating-gate transistors in general have short write-lifetimes, on the order of 105 writes to any particular bit.
Starting around 2000, demand for ever-greater quantities of flash have driven manufacturers to use only the latest fabrication systems in order to increase density as much as possible.
Although fabrication limits are starting to come into play, new "multi-bit" techniques appear to be able to double or quadruple the density even at existing line widths.
Unlike RAM devices, F-RAM retains its data memory when power is shut off or interrupted, due to the PZT crystal maintaining polarity.
Due to this crystal structure and how it is influenced, F-RAM offers distinct properties from other nonvolatile memory options, including extremely high endurance (exceeding 1016 access cycles for 3.3 V devices), ultra low power consumption (since F-RAM does not require a charge pump like other non-volatile memories), single-cycle write speeds, and gamma radiation tolerance.
Another approach to see major development effort is magnetoresistive random-access memory, or MRAM, which uses magnetic elements and in general operates in a fashion similar to core, at least for the first-generation technology.
Considered a dark horse for some time, in 2006 Samsung announced the availability of a 512 Mbit part, considerably higher capacity than either MRAM or FeRAM.
The areal density of these parts appears to be even higher than modern flash devices, the lower overall storage being due to the lack of multi-bit encoding.
Intel and Micron Technology had a joint venture to sell PRAM devices under the names 3D XPoint, Optane and QuantX, which was discontinued in July 2022.
Although it was planned to introduce Millipede as early as 2003, unexpected problems in development delayed this until 2005, by which point it was no longer competitive with flash.
Such devices are claimed to have the advantage that they utilise the same technology as HKMG (high-L metal gate) based lithography, and scale to the same size as a conventional FET at a given process node.