By: Ungo (a.delete@this.b.c.d.e), November 25, 2022 2:26 am
Room: Moderated Discussions
Joern Engel (joern.delete@this.purestorage.com) on November 24, 2022 11:00 pm wrote:
> jokerman (jo.delete@this.ker.man) on November 24, 2022 12:13 pm wrote:
> > For NAND flash, to change 0 to 1, erasing and reprogramming of the whole block is needed.
> > Transisitons from 1 to 0 are easier to do.
>
> That used to be true for NOR flash, but never worked for NAND. Once you introduce
> ECC, the checksum will have to flip bits both ways to match new data.
So what? The need for ECC didn't magically change the nature of flash. High-density NAND is still flash, and therefore still has the asymmetry jokerman described: programming operations may set individual cells to 0, but returning any cell to 1 requires erasing a much larger block.
(I'm talking here as if SLC is the only thing which exists. The principle still holds true with multi-level technology, it just gets more complicated to talk about. Programming can only alter the state of charge of a cell in one direction; to go in the other direction requires an erase.)
The only enhancement in NAND flash for the sake of ECC is that pages are larger than the nominal "sector size" of the flash memory, providing some extra bytes to store the ECC syndrome. (Or whatever else you feel like putting there. The flash memory doesn't care what you do with the extra storage, it isn't responsible for error correction.)
> jokerman (jo.delete@this.ker.man) on November 24, 2022 12:13 pm wrote:
> > For NAND flash, to change 0 to 1, erasing and reprogramming of the whole block is needed.
> > Transisitons from 1 to 0 are easier to do.
>
> That used to be true for NOR flash, but never worked for NAND. Once you introduce
> ECC, the checksum will have to flip bits both ways to match new data.
So what? The need for ECC didn't magically change the nature of flash. High-density NAND is still flash, and therefore still has the asymmetry jokerman described: programming operations may set individual cells to 0, but returning any cell to 1 requires erasing a much larger block.
(I'm talking here as if SLC is the only thing which exists. The principle still holds true with multi-level technology, it just gets more complicated to talk about. Programming can only alter the state of charge of a cell in one direction; to go in the other direction requires an erase.)
The only enhancement in NAND flash for the sake of ECC is that pages are larger than the nominal "sector size" of the flash memory, providing some extra bytes to store the ECC syndrome. (Or whatever else you feel like putting there. The flash memory doesn't care what you do with the extra storage, it isn't responsible for error correction.)
| Topic | Posted By | Date |
|---|---|---|
| Is 1 more expensive than 0? | Andrey | 2022/11/21 05:23 AM |
| Is 1 more expensive than 0? | Juha Lainema | 2022/11/21 06:15 AM |
| Is 1 more expensive than 0? | Adrian | 2022/11/21 07:21 AM |
| Is 1 more expensive than 0? | anon2 | 2022/11/21 05:29 PM |
| switching between 0 and 1 is what consumes power | Heikki Kultala | 2022/11/21 07:23 AM |
| Thank you all for your answers. (NT) | Andrey | 2022/11/21 08:29 AM |
| Is 1 more expensive than 0? | Foyle | 2022/11/21 08:58 AM |
| Is 1 more expensive than 0? | Michael S | 2022/11/21 10:51 AM |
| Is 1 more expensive than 0? | Captain Obvious | 2022/11/21 11:29 AM |
| obvious stuff | anonymou5 | 2022/11/21 02:25 PM |
| obvious stuff | Andrey | 2022/11/21 02:50 PM |
| obvious stuff | Michael S | 2022/11/21 03:43 PM |
| SRAM is bistable | Anon | 2022/11/21 10:50 AM |
| SRAM is bistable | Andrew Clough | 2022/11/22 05:53 AM |
| NAND Flash 1 and 0 | jokerman | 2022/11/24 01:13 PM |
| NAND Flash 1 and 0 | Joern Engel | 2022/11/25 12:00 AM |
| NAND Flash 1 and 0 | Ungo | 2022/11/25 02:26 AM |
| The ECC needs to be stored. as ones ane zeroes (NT) | Heikki Kultala | 2022/11/25 08:31 AM |
| The ECC needs to be stored. as ones ane zeroes | anon2 | 2022/11/25 05:07 PM |
| The ECC needs to be stored. as ones ane zeroes | Heikki Kultala | 2022/11/26 12:48 AM |
| The ECC needs to be stored. as ones ane zeroes | anon2 | 2022/11/26 02:00 AM |