Flash memory (page 3)
Types of Flash memory devices.
Flash cards use flash memory chips to store and retrieve the data. Generally, the linear cards use DINOR and NOR flash chips, while ATA PC cards use AND and NAND flash chips. Those chips are electrically programmable and re-programmable non-volatile solid-state data storage devices. These chips are similar to EEPROM (Electrically Erased Programmable ROM), except for the write operation.
EEPROM chip automatically erases the data/word at the specified address when the write operation is initiated. Unlike to EEPROM, an external controller flashes not one data/word in the Flash chip, but the entire block of data (from 512 B to the entire chip). Therefore, when compared to EEPROM, Flash memory offers lower flexibility, but higher performance, smaller energy consumption, and significant cost advantage.
NOR NOR represents the earliest flash design. NOR flash memory has large sector size and cell size, high-speed rewrite and high-speed random data access. NOR devices use energy consuming hot electron injection for data writing and tunnel release for erasing. Storage capacity (called density) for NOR flash chips is currently in the range from 64 Kb to 8 Mb. One disadvantage of NOR is that they are difficult to scale up to higher capacities.
NAND NAND flash chips are serial access devices with high storage capacity, single voltage (3.3 V or 5 V) operation, small block size, small cell size, and high durability. NAND use tunnel injection for writing and tunnel release for erasing, which is a power-saving technique. Storage capacity (called density) for NOR flash chips is currently in the range from 500 Kb to 8 Mb.
DINOR (Divided bit-line NOR) DINOR flash chips (introduced by Mitsubishi) have high random data access, single voltage supply (3.3 V or 2.7 V), fast block erase, large block size, multi-sector erase capabilities, and low power consumption using tunnel injection/tunnel release for write and erase. Storage capacity (called density) for DINOR is currently in the range from 1 MB to 2 MB.
AND AND flash chips (introduced by Hitachi) is a serial access device combining the best of the NOR and NAND devices. It has fast erase, single voltage supply operation, very high capacity, low power consumption (writing by tunnel injection and erasing by tunnel current release), and small block size. It offers multiblock erase and auxiliary Byte redundancy for ECC. AND flash chips are optimized for high-capacity storage devices such as ATA Flash PC cards. Devices with more than 32 MB of storage capacity are available.
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