Thursday, November 03, 2011

Types of 'Flash Memory'

"Flash Memory", or EEPROM (Electrically Erasable Programmable Read Only Memory), is at the heart of much of the "silicon revolution" of the last 10 years.

How is it packaged and made available to consumers or system builders/designers?

Mobile appliances are redefining Communications and The Internet, precisely because of the low-power, high-capacity and longevity - and affordable price -  of modern Flash Memory.

There are many different Flash Memory configurations: NAND, NOR, SLC, MLC, ...
This piece isn't about those details/differences but the in how they are packaged and organised.
What technology does what/has what characteristics is out there on the InterWebs.

Most Flash Memory chips are assembled into different packaging for different uses at different price points. Prices are "Retail Price (tax paid)" from a random survey of Internet sites:
  • Many appliances use direct-soldered Flash Memory are their primary or sole Persistent Datastore.
    The genesis of this was upgradeable BIOS firmware. Late 1990's?
    Per-Gb pricing not published: approx. derivable from model price differences.
  • Commodity 'cards' used in cameras, phones and more: SD-card and friends.
    Mini-CD and Micro-SD cards are special cases and attract a price premium.
    Some 'high-performance' variants for cameras.
  • USB 'flash' or 'thumb drives':
  • High-end camera memory cards: Compact Flash (CF). The oldest mass-use format?
    IDE/ATA compatible interface. Disk drive replacement for embedded systems.
    Fastest cards are 100MB/sec (0.8Gbps). Max is UDMA ATA, 133MB/sec.
    Unpublished Bit Error Rate, Write Endurance, MTBF, Power Cycles, IO/sec.
  • SATA 2.5" SSD (Solid State Drives). Mainly 3Gbps and some 6Gbps interfaces.
    MTBF: 1-2M hours,
    Service Life: 3-5 years at 25% capacity written/day.
    IO/sec: 5,000 - 50,000 IO/sec [max seen: 85k IO/sec]
    BER: "1 sector per 1015-16 bits read"
    sustained read/write speed: 70-400MB/sec . (read often slowest)

    Power: 150-2000W active, 75-500mW idle
    32Gb - 256GB @ A$1.50-$2.50/Gb.
  • SATA 1.8" SSD. Internal configuration of some 2.5" SSD's.
    Not yet widely available.
  • SAS (Serial Attached SCSI) 2.5" drives.
    not researched. high-performance, premium pricing.
  • PCI "SSD". PCI card presenting as a Disk Device.
    Multiple vendors, usual prices ~A$3-4/Gb. Sizes 256Gb - 1Tb.
    "Fusion-io" specs quoted by Dell. Est A$20-25/Gb. [vs ~$5/Gb direct]
    640GB (Duo)
    NAND Type: MLC (Multi Level Cell)
    Read Bandwidth (64kB): 1.0 GB/s
    Write Bandwidth (64kB): 1.5 GB/s
    Read IOPS (512 Byte): 196,000
    Write IOPS (512 Byte): 285,000
    Mixed IOPS (75/25 r/w): 138,000
    Read Latency (512 Byte): 29 μs
    Write Latency (512 Byte): 2 μs
    Bus Interface: PCI-Express x4 / x8 or PCI Express 2.0 x4
  • Mini-PCIe cards, Intel:  40 and 80Gb. A$3/Gb
    Intel SSD 310 Series 80GB mini PCIe

    * Capacity: 80 GB,
    * Components: Intel NAND Flash Memory Multi-Level Cell (MLC) Technology
    * Form Factor, mini PCIe, mSATA, Interface,
    * Sequential Read - 200 MB/s, Sequential Write - 70 MB/s,
    * Latency - Read - 35 µs, Latency - Write - 65 µs,
    * Lithography - 34 nm
    * Mean Time Between Failures (MTBF) - 1,200,000 Hours
Roughly, prices increase with size and performance.
The highest density chips, or leading edge technology,  cost a premium.
As do high-performance or "specialist" formats:
  • micro-SD cards
  • CF cards
  • SAS and PCI SSD's.

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