Storage Element

NAND Flash Memory

USB Flash drive Project Mohamed Fadel Buffon

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

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

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

NAND Flash || NOR Flash

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

Commands

Read Operation

Write Operation

Storing

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Types of NAND Flash

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.

SLC NAND Flash

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

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}).

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

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.

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

Reference• “NAND Flash FAQ” from Eureka Technology.

The End

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