What happens when a NAND flash page is empty?
[* Technical note: Ok so actually when a NAND flash page is empty it is all binary ones, e.g. 11111111. A program operation sets any bit with the value of 1 to 0, so for example 11111111 could become 11110000. This means that later on it is still possible to perform another program operation to set 11110000 to 00110000 for example.
Which is the bit line in a NAND flash?
In a NAND flash, the bit line will be 1, if and only if the selected floating gat MOSFET has a high threshold voltage. The cells are in parallel or series, except the gate. Some NOR flash also have a page buffer, to further improve the sequential read speed.
How many words are in a block of NAND flash?
In a typical NAND flash there are 32-64 word lines per block, therefore, neglecting the bit-line capacitances, the time might be about 30-60 times larger than NOR (given the same number of word lines). To improve this, a page buffer (a small static ram) is inserted on NAND flash (see also note 3).
What happens when you erase a block in Flash?
If you were to erase the block every time you wanted to change the contents of a page, your flash would wear out very quickly. So a far better alternative is to simply mark the old page (containing the unchanged data) as INVALID and then write the new, changed data to an empty page.
What happens to the pages on a flash card?
When your flash device arrives fresh from the vendor, all of the pages are “empty”. The first thing you will want to do, I’m sure, is write some data to them – which in the world of memory chips we call a program operation. As discussed, these program operations take place at the page level.
Is the entire page erased before writing just a few bytes?
Partial-page programming, non-sequential pages programming within the block, excessive read per block without erase as well as non-equal number of read operation within a single block increase number of the read disturb errors.” — Michal Jedrak. “NAND Flash memory in embedded systems”.
When do pages need to be erased in Flash?
Since a block needs to be erased before it can be programmed again (*sort of, I’m generalising to make this easier), all of the pages in a block need to be candidates for erasure before this can happen. Program / Erase Cycles. When your flash device arrives fresh from the vendor, all of the pages are “empty”.
Why does erase only happen in a block?
To answer why erase only happens in blocks on a physical level, the actual NAND cells are implemented in a P-well within a deep N-well. Because erase involves setting the substrate to a high voltage so that electrons can tunnel out through F-N tunneling, all the cells within a P-well are set to the same substrate voltage.
How many NAND memory chips are there in the world?
There are thousands of different NAND chips available, each potentially with slightly different instruction sets, block/page sizes, performance characteristics etc. The package is the memory chip, i.e. the black rectangle with little electrical connectors sticking out of it.