<P> For those types of ROM that can be electrically modified, writing speed has traditionally been much slower than reading speed, and it may need unusually high voltage, the movement of jumper plugs to apply write - enable signals, and special lock / unlock command codes . Modern NAND Flash achieves the highest write speeds of any rewritable ROM technology, with speeds as high as 10 GB / s, this has been enabled by the increased investment in both consumer and enterprise solid state drives and flash memory products for higher end mobile devices . On a technical level the gains have been achieved by increasing parallelism both in controller design and of storage, the use of large DRAM read / write caches and the implementation of memory cells which can store more than one bit (DLC, TLC and MLC). The latter approach is more failure prone but this has been largely mitigated by overprovisioning (the inclusion of spare capacity in a product which is visible only to the drive controller) and by increasingly sophisticated read / write algorithms in drive firmware . </P> <P> Because they are written by forcing electrons through a layer of electrical insulation onto a floating transistor gate, rewriteable ROMs can withstand only a limited number of write and erase cycles before the insulation is permanently damaged . In the earliest EPROMs, this might occur after as few as 1,000 write cycles, while in modern Flash EEPROM the endurance may exceed 1,000,000 . The limited endurance, as well as the higher cost per bit, means that Flash - based storage is unlikely to completely supplant magnetic disk drives in the near future . </P> <P> The timespan over which a ROM remains accurately readable is not limited by write cycling . The data retention of EPROM, EAROM, EEPROM, and Flash may be limited by charge leaking from the floating gates of the memory cell transistors . Leakage is accelerated by high temperatures or radiation . Masked ROM and fuse / antifuse PROM do not suffer from this effect, as their data retention depends on physical rather than electrical permanence of the integrated circuit, although fuse re-growth was once a problem in some systems . </P> <P> The contents of ROM chips can be extracted with special hardware devices and relevant controlling software . This practice is common for, as a main example, reading the contents of older video game console cartridges . Another example is making backups of firmware / OS ROMs from older computers or other devices - for archival purposes, as in many cases, the original chips are PROMs and thus at risk of exceeding their usable data lifetime . </P>

Write a short note on ram and rom