This document discusses NAND flash memory, which is used in USB flash drives for portable storage. It describes how NAND flash works, including that it has a controller that sends commands serially to program and read the flash. Issues with NAND flash include bad blocks, long access times since it is not random access, and short lifetimes due to being programmable. Technologies like wear leveling aim to extend the lifetime by distributing writes across blocks.

1. USB Flash drive Project Mohamed Fadel Buffon
Storage Element
NAND Flash Memory

2. Agenda
 What is NAND Flash?
What does NAND Flash Controller do?
What is ONFI?
What are NAND Flash issues?
What is wear leveling Technology?

3. What is NAND Flash?
• Non Volatile Memory.
• Programmable Memory.
• Portable Storage.

4. Diff. between NAND Flash & Others
• Serial Storage device.
• Long Access Time.
• Not RAM.

5. NAND Flash || NOR Flash

6. What does NAND Flash Cont. Do?
• Send Commands Serially (as packets).
• Generate ECC Information.

7. Commands

8. Read Operation

9. Write Operation

10. Storing
0
x
x

11. Types of NAND Flash

12. Types of NAND Flash
• MLC offers higher storage density.
• But MLC is slower and less robust.
• MLC  10,000 erase/program cycle.
• SLC  100,000 erase/program cycle.

13. SLC NAND Flash

14. What is ONFI?
• Open Standard for device level NAND Flash interface.
• Supported by new NAND Flash devices.

15. ECC
• Is a good way to recover the wrong value.
• Can be implemented by:
– Hardware (Faster).
– Software.
• SLC  1-bit ECC correction per 512 bytes (which
mean 24 ECC bits {Hamming Code}).

16. What are NAND Flash issues?
• Bad Blocks.
• Long Access Time.
• No Random Access.
• Short Life-time.

17. What is wear leveling?
• Divide Data to Segments.
• Distribute Segments on multi-pages.
• Re-map the logical address to physical address.
• Adv:
– Extend the NAND Flash life-time.

18. What is RAM shadowing?
• Like External Cache Memory.
• Reasons:
– Limit erase/program cycle.
– Slow speed (compared to SDRAM).

19. Reference
• “NAND Flash FAQ” from Eureka Technology.

20. The End
Questions??