Okay, i have looped in comp.arch.embedded. Yeah, I have been searching regarding this & got other links but did not get a link that clearly conveys this info and hence this query.
After lot of searches, got the below links -
It seems that Flash memory uses in-circuit wiring to apply the electric field either to the entire chip or to predetermined sections known as blocks. This erases the targeted area of the chip, which can then be rewritten. Flash memory works much faster than traditional EEPROMs because instead of erasing one byte at a time, it erases a block or the entire chip, and then rewrites it.
This link is good ! I understand that erasure operation is done through Quantum tunneling.
Interesting to know that in NAND-flash, cells are connected in series resembling a NAND gate, and so the name. The series connection prevents the cells from being programmed individually. These cells must be read in series.
So, it finally boils down to the design of flash memory that has dependency on predetermined sections known as BLOCKS or entire chip for its in-circuit wiring that applies electric field either to the entire chip or to predetermined sections known as BLOCKS !!
Thx, Karthik Balaguru