On 1/6/15 2:00 PM, math-fun-request@mailman.xmission.com wrote:
From: Whitfield Diffie <whitfield.diffie@gmail.com> Subject: Re: [math-fun] NAND flash memory
... an erase operation on such a block resets the block to all 1's. If erase resents the bits of the block to all the same value, why not call it zero?
I guess it's like why they call it "NAND" flash instead of NOR flash (there is NOR flash already): they're referring to some particular point in the circuit being at the conventional voltage for "1". (And the conventional meaning of a NAND gate vs. NOR gate, even though the two do the same job, just inverted.) Similarly, lines within or between chips sometimes have names like "not-reset", because the engineers have to know which voltage (the low one) means reset. In old TTL chips, making something zero took power; if you left a line disconnected, a resistor on the input would pull it up to one. Probably at some level of the software of the control computer on the chip, the meaning gets inverted, so that as a user you can say, "clear all blocks to zero" and the corresponding physical blocks get "reset to 1." Again, just guessing. That weird overlap between electrical and actual boolean thinking always used to bother me. --Steve