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by Thomas Coughlin

  • Common flash memory cards
    • The most common flash memory products currently in use are SD cards and derivative products (e.g. mini and micro-SD cards)
    • Some compact flash used for professional applications (such as DSLR cameras)
  • Evolution of leading flash formats
    • Standardization –> market expansion
    • Market expansion –> volume
    • iNAND –> focus is on enabling embedded X3
    • iSSD –> ideal for thin form factor devices
  • Flash memory applications
    • Phones are the #1 user of flash memory
    • Flash memory is used as embedded and removable storage in many mobile applications
    • Flash memory is being used in computers as USB sticks and SSDs
    • Possible use of flash memory in computer combined with HDDs (hybrid HDDs and paired or dual storage computers)
  • It can be a removable card or an embedded card
  • These devices can only handle a specific number of writes
  • Flash memory reads considerably quicker than hard drives
  • Hybrid and dual storage in computers
    • SSDs can provide fast performance but they are expensive
    • HDDs can provide cheap storage but they are relatively slow
    • Combining some flash memory with a HDD can provide costs close to those of HDDs and performance close to flash memory
      • Seagate Momentus XT hybrid HDD
      • Various dual storage offerings putting flash memory with HDDs
  • Other common flash memory devices
    • USB sticks
      • All forms and colors
      • Used for moving files around
      • Some sold with content on them (Sony Movies on USB sticks)
    • Solid State Drives (SSDs)
  • Floating Gate Flash Memory Cell
    • When a bit is programmed, electrons are stored upon the floating gate
    • This has the effect of offsetting the charge on the control gate of the transistor
    • If there is no charge upon the floating gate, then the control gate’s charge determines whether or not a current flows through the channel
    • A strong charge on the control gate assumes that no current flows. A weak charge will allow a strong current to flow through.
  • Similar to HDDs, flash memory must provide:
    • Bit error correction
    • Bad block management
  • NAND and NOR memories are treated differently when it comes to managing wear
  • In many NOR-based systems no management is used at all, since the NOR is simply used to store code, and data is stored in other devices. In this case, it would take a near-infinite amount of time for wear to become an issue since the only time the chip would see an erase/write cycle is when the code in the system is being upgraded, which rarely if ever happens over the life of a typical system.
  • NAND is usually found in very different application than is NOR
  • Flash memory wears out
    • This is expected to get worse over time
  • Retention: Disappearing data
    • Bits fade away
      • Retention decreases with increasing read/writes
      • Bits may change when adjacent bits are read
      • Time and traffic are concerns
    • Controllers typically groom read disturb errors
      • Like DRAM refresh
      • Increases erase/write frequency
  • Application characteristics
    • Music – reads high / writes very low
    • Video – r high / writes very low
    • Internet Cache – r high / writes low
  • On airplanes
    • Many consumers now have their own content viewing devices – do they need the airlines?
    • Is there a way to offer more to consumers, especially with their own viewers
      • Additional special content
      • tie into airplane network
      • access to electrical power, internet
    • Should there be fixed embedded or removable storage for on-board airline entertainment?
    • Is there a way to leverage personal and airline viewers and content in new and entertaining ways?
Posted on Tuesday, February 22, 2011 12:36 PM | Back to top

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