    flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. introduced by toshiba in 1984, flash memory was developed from eeprom (electrically erasable programmable read-only memory). there are two main types of flash memory, which are named after the nand and nor logic gates. the internal characteristics of the individual flash memory cells exhibit characteristics similar to those of the corresponding gates. where as eproms had to be completely erased before being rewritten, nand type flash memory may be written and read in blocks (or pages) which are generally much smaller than the entire device. nor type flash allows a single machine word (byte) to be writtento an erased locationor read independently. the nand type is primarily used in main memory, memory cards, usb flash drives, solid-state drives, and similar products, for general storage and transfer of data. the nor type, which allows true random access and therefore direct code execution, is used as a replacement for the older eprom and as an alternative to certain kinds of rom applications, whereas nor flash memory may emulate rom primarily at the machine code level; many digital designs need rom (or pla) structures for other uses, often at significantly higher speeds than (economical) flash memory may achieve. nand or nor flash memory is also often used to store configuration data in numerous digital products, a task previously made possible by eeprom or battery-powered static ram. one significant disadvantage of flash memory is the finite amount of read/write cycles in a specific block. example applications of both types of flash memory include personal computers, pdas, digital audio players, digital cameras, mobile phones, synthesizers, video games, scientific instrumentation, industrial robotics, medical electronics, and so on. in addition to being non-volatile, flash memory offers fast read access times, as fast as dynamic ram, although not as fast as static ram or rom. its mechanical shock resistance helps explain its popularity over hard disks in portable devices, as does its high durability, being able to withstand high pressure, temperature, immersion in water, etc. although flash memory is technically a type of eep
Computer_memory Japanese_inventions Non-volatile_memory Solid-state_computer_storage_media