Non volatile memory in cell phones

Mobile Handsets (cell phones) employ a type of solid state – non volatile – memory known as flash memory to store such things as SMS,call records pictures and videos. There are two types of flash memory that are commonly used – NOR and NAND.

NOR Memory was invented by Intel and its strengths lie in its fast read, and its ability to run applications in place (XIP) rather than copying the application into RAM. However NOR memory suffers from low write and erase performance (5s) and is expensive.

NAND competes with NOR memory in that it is effective in high storage capacities, and has fast write and erase rates(4ms) – it is also cheaper than NOR . However, NAND memory requires that there be some sort of flash memory management in place and has special requirements for a system interface.

There are differences in life span of the two types of memory. NAND has the longer life span at somewhere around one million erase cycles compared to NOR’s one hundred thousand.

NOR also allows for its entire media to be addressed where NAND requires a complicated I/O interface that can be further complicated by vendor or device differences.

NOR and NAND both can fall prey to “bit flipping”, where a bit is either reversed or is reported reversed. It is rare but more common in NAND. Error detection or correction algorithms must be employed and NAND vendors all recommend this be done. Bit flipping isnt as critical for multimedia storage (a task for which NAND is commonly employed), but it is for operating system or sensitive information storage.

Used in cell phones NOR memory is used as the code storage media – for things such as the OS, default applications etc – while the cheaper, higher capacity NAND is used for storing user data such as pictures videos and the like.


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