METHOD FOR SELECTIVE ERASING AND PARALLEL PROGRAMMING/VERIFYING OF CELL BLOCKS IN A FLASH EEPROM SYSTEM

A system of Flash EEprom memory chips with controlling circuits serves as non-volatile memory such as that provided by magnetic disk drives. A chunk of user data is programmed into a group of memory cells in parallel, the programming of individual memory cells being terminated when they are determined to have reached desired threshold level ranges while the programming of other memory cells continues. Other improvements include selective multiple sector erase, in which any combinations of Flash sectors may be erased together. Selective sectors among the selected combination may also be de-selected during the erase operation. Another improvement is the ability to remap and replace defective cells with substitute cells. The remapping is performed automatically as soon as a defective cell is detected. When the number of defects in a Flash sector becomes large, the whole sector is remapped. Yet another improvement is the use of a write cache to reduce the number of writes to the Flash EEprom memory, thereby minimizing the stress to the device from undergoing too many write/erase cycling.