Memory can be split into two main categories: volatile and nonvolatile. Volatile memory loses its content when the system is powered off. Nonvolatile memory does not lose its data when the system or device is turned off. RAM is an example of volatile memory. ROM is an example of non-volatile memory. Different types of ROM are Programmable (PROM), Erasable Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM).
Flash memory is a type of EEPROM. The read/write behaviours of flash memory is very different than that of other programmable memories, such as volatile ram and magnetic disks. The most important characteristics of Flash memory are
1. Memory cells in a flash device can be written to only a limited number of times, between 10,000 and 1,000,000, after which they wear out and become unreliable.
2. Flash devices are available in two major types
NOR Flash -which is directly accessible by the processor.
NAND Flash - which is addressable only through a separate controller.
3. Flash chips are arranged into memory blocks. Resetting bits from zero to one( Erase) cannot be done individually, but only by erasing a complete block. Erase block sizes of NOR and NAND Flashes are different.
4. Write operations of a flash can only clear bits (change their value from 1 to 0). The only way to set bits (change their value from 0 to 1) is to erase an entire region memory, called erase units or memory blocks.
5. Flash Chip users should use a process known as "wear levelling" to ensure the even distribution of usage of each block. Means a single block should not become unusable before the Flash chip.
NAND Flashes are further divided into pages which are typically 512 bytes in size.
Flash memory is a type of EEPROM. The read/write behaviours of flash memory is very different than that of other programmable memories, such as volatile ram and magnetic disks. The most important characteristics of Flash memory are
1. Memory cells in a flash device can be written to only a limited number of times, between 10,000 and 1,000,000, after which they wear out and become unreliable.
2. Flash devices are available in two major types
NOR Flash -which is directly accessible by the processor.
NAND Flash - which is addressable only through a separate controller.
3. Flash chips are arranged into memory blocks. Resetting bits from zero to one( Erase) cannot be done individually, but only by erasing a complete block. Erase block sizes of NOR and NAND Flashes are different.
4. Write operations of a flash can only clear bits (change their value from 1 to 0). The only way to set bits (change their value from 0 to 1) is to erase an entire region memory, called erase units or memory blocks.
5. Flash Chip users should use a process known as "wear levelling" to ensure the even distribution of usage of each block. Means a single block should not become unusable before the Flash chip.
NAND Flashes are further divided into pages which are typically 512 bytes in size.
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