introduction to flash memory l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Introduction to Flash Memory PowerPoint Presentation
Download Presentation
Introduction to Flash Memory

Loading in 2 Seconds...

play fullscreen
1 / 24

Introduction to Flash Memory - PowerPoint PPT Presentation


  • 775 Views
  • Uploaded on

Introduction to Flash Memory. 2006. 11. 15. Mobile Embedded System Lab. Kiseok, Choi. Table of Contents. Stateless PC Flash Memory Basics NAND vs. NOR SLC vs. MLC NAND Flash Memory FTL (Flash Translation Layer) An FTL Design Based on Log Blocks The Log Block The Map Block

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Introduction to Flash Memory' - salena


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
introduction to flash memory

Introduction to Flash Memory

2006. 11. 15.

Mobile Embedded System Lab.

Kiseok, Choi

table of contents
Table of Contents
  • Stateless PC
  • Flash Memory Basics
    • NAND vs. NOR
    • SLC vs. MLC
    • NAND Flash Memory
  • FTL (Flash Translation Layer)
    • An FTL Design Based on Log Blocks
      • The Log Block
      • The Map Block
    • SSD (Solid State Disk)
  • State-of-the-art Technologies
  • Research Issues
  • Summary
stateless pc
Stateless PC
  • Definition : The PC that has no states, especially non-volatile states.
stateless pc4
Stateless PC

Remove non-volatile states

Current PC

Stateless PC

State

  • What’s in the portable storage?
  • Operating Systems
  • File Systems
  • Private data
  • Applications
stateless pc5
Stateless PC
  • Storage for the states
    • Flash memory is a good solution for the physical storage.
  • Why flash memory?
    • Faster access
    • Shock / Temperature resistance
    • Smaller size
    • Lighter weight
    • Lower power
    • Noiseless (0dB)
flash memory basics
Flash Memory Basics
  • Flash memory
    • A non-volatile semiconductor memory device
    • Key feature :
      • To overwrite data, the memory cell should be erased first.
  • Kinds of flash memory
    • NOR
      • Introduced by Intel in 1988
      • Randomly access data, like a computer’s main memory
      • Use for executing program code
    • NAND
      • Introduced by Toshiba in 1989
      • Smaller and denser.

→ NAND is better at storing data.

      • Faster erase and write time

NOR

NAND

nand vs nor
NAND vs. NOR

Pros of NAND

Pros of NOR

1. Smaller cell size

2. Limited bad blocks allowed

3. Fast writing

4. Lower power consumption

1. Fast random (read) access

We focus on

the NAND flash memory!

Cons of NAND

Cons of NOR

1. Slow random (read) access

1. Larger cell size

2. No bad blocks are allowed

3. Slow writing

4. Higher power consumption

For Code Storage

For Mass Storage

nand flash memory
NAND Flash Memory
  • Organization of NAND flash memory
    • Small-block flash memory
      • Each page is (512 + 16) bytes long
      • 32 pages in each block
    • Large-block flash memory
      • Each page is (2048 + 64) bytes long
      • 64 pages in each block
  • Page layout for small-block flash memory

Block 0

Block 1

Block n-1

Page 0

512

16

Page 1

  • Page layout for large-block flash memory

2048

64

Page m-1

chip

Main Area

Spare Area

nand flash memory9
NAND Flash Memory
  • Primitive operations of NAND flash memory
    • Read page
      • (chip #, block #, page #)
      • ~20 us
    • Write (program) page
      • (chip #, block #, page #)
      • ~200 us
    • Erase block
      • (chip #, block #)
      • ~2 ms
ftl flash translation layer

Flash Memory

Flash Memory

Flash Memory

Flash Memory

FTL (Flash Translation Layer)

File System

File System

Read Sectors

Write Sectors

Read Sectors

Write Sectors

Mismatch!

Read Sectors

Write Sectors

Read

Write

Erase

FTL

+

Device Driver

Device Driver

+

+

ftl flash translation layer11
FTL (Flash Translation Layer)
  • Definition
    • Software layer that makes flash memory appear to the system like a disk drive
  • Challenges in FTL
    • Asymmetry in read and write speeds
    • No overwrite is allowed without erasing
ftl basics
FTL basics
  • Read request from upper layer
    • No problem.
  • Write request from upper layer
    • There is a problem.
      • Erase operation must be done first (the erase operation is performed in a block unit) to overwrite data.
an ftl design based on log blocks
An FTL Design Based on Log Blocks
  • Background
    • 2 kinds of blocks
      • Data block: block level managed block (most)
      • Log block: page level managed block (a few)
        • Temporary storage for small size writes to data blocks

Data Block

Log Block

Write!

Data is written to

the log block

valid

valid

valid

valid

an ftl design based on log blocks14
An FTL Design Based on Log Blocks
  • Whenever the log block is full,
    • We need to merge the data block and the log block.
an ftl design based on log blocks15
An FTL Design Based on Log Blocks
  • Merge Operation
    • Log Block Merge

Data Block

Data Block

Free Block

Log Block

valid

valid

valid

valid

valid

valid

valid

valid

Free blocks

an ftl design based on log blocks16
An FTL Design Based on Log Blocks
  • Merge Operation (cont’d)
    • Log Block Switch

Data Block

Data Block

Log Block

valid

valid

valid

valid

valid

valid

valid

valid

Free blocks

an ftl design based on log blocks17
An FTL Design Based on Log Blocks
  • Where is the mapping information?
    • Mapping information : logical address to physical address
    • It is stored in map blocks.
map block
Map Block
  • The Map Block
    • Where to store the mapping information
      • Previous scheme: each page/block in the associated spare area in the form of logical address tags
        •  requiring scanning of the entire space of flash memory to collect logical address tags
      • Map blocks: dedicated blocks to enable faster startup and on-demand fetching
        •  using map blocks in a round robin manner
      • Map Directory: the map of the mapping table in SRAM and is used to locate each portion of the mapping table stored in map blocks
        •  the map directory is stored in a reserved area of the flash memory
ssd solid state disk
SSD (Solid State Disk)
  • The disk that uses the semiconductor as storage
    • DRAM-based
    • Flash-based
      • P-ATA / S-ATA interface
      • FTL
      • NAND flash memory
  • Target markets
    • Enterprise server storage
    • Mainstream PC storage
ssd solid state disk20
SSD (Solid State Disk)
  • HYDRA project
    • 2005.9 ~
    • Mtron + SNU
    • 3.5 inch engineering sample already released

(PCMark 04)

state of the art technologies
State-of-the-art Technologies
  • In the perspective of the pure NAND
    • Copy-back operation
      • Using internal data copies, data transfer overhead can be removed (used for merge operations).
    • Cache programming
      • Besides the page register, there’s a cache register.
      • Using double buffering, throughput can be increased.
state of the art technologies22
State-of-the-art Technologies
  • In the perspective of new-typed NAND
    • Hybrid systems are proposed.
      • Pure NAND is not well suitable for running applications
      • dynamic/static RAM component + NAND
        • OneNAND = SRAM + NAND
      • High performance (read/write)
      • More expensive and less energy efficient
research issues
Research Issues
  • How to handle of bad blocks
    • Initial bad block and run-time bad block
    • Usually handled by the “bad block table” method
  • Wear-Leveling
    • There’s a limit on the number of erases
    • About 100,000 times
    • Need to erase flash memory blocks evenly
  • How to improve performance effectively
summary
Summary
  • Stateless PC will replace the current PC in the future.
  • Reliable & fast portable storage is required for non-volatile storage of states.
  • Flash memory is a good choice for storage.
  • So the research focused on how to improve flash memory performance/capacity/durability is required.