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Serial ATA
Last updated: 9/8/01

Q.  What is a Serial ATA disk drive?

To put it in a nutshell, the ATA Serial standard is a simplified packet switching network between a motherboard or computer backplane and a disk drive.  It employs balanced voltage (differential) amplifiers and four wires/two pairs (transmission line) to connect transmitters to receivers in a manner similar to the 100BASE-TX Ethernet.  The pins in the spec are labeled TX+, TX-, RX+, and RX- just like they are in the twisted-pair Ethernet.  There is no specification for a standard ATA Serial cable (just electrical requirements it must meet), but each pair of wires will probably be parallel and shielded (there is a cable construction example in the spec.).  There is a separate power cable.  Here are some brief highlights of this recent technology:

  • Scalable performance… Three stages over ten years… Starts at 1.5 Gigabits per second, then 3 Gbps, and ultimately 6 Gbps (six times faster than the current ATA/100 standard).  These numbers are right in the spec.
  • 100% software compatible with current operating systems and does not require any new drivers/changes to existing operating systems.
  • Primarily for inside-the-box drive connections.  Maximum cable length is 1 meter.  No cameras/scanners/printers.
  • Supports all ATA and ATAPI devices, including CDs, DVDs, tape
    devices, high capacity removable devices, zip drives, and CD-RWs.
  • Drives can be attached by cable or plugged directly into backplanes.
  • More reliable connectors with smaller plugs and a lower pin-count.
  • Plugs are blind mated (can plug them in blindfolded without making an error).
  • No drive jumpers or terminators, one drive per cable, Plug ‘n Play (Prey?).
  • Drives can be hot plugged—installed with the computer on.
  • Smaller cables (thin, flexible) that are simple to route and install.  The data cable has 4 conductors.
  • Smaller cables will allow much better case ventilation (and access/visibility).
  • Less complex trace runs on motherboards; will permit smaller motherboards.
  • ATA Serial interface to be incorporated into the motherboard chipsets.
  • Favorable (low) voltages and efficient power delivery.
  • Power management and power consumption suitable for mobile use.
  • Light protocol minimizes overhead latencies.
  • Asynchronous only (no isochronous requirements).
  • No peer-peer transfer support (to/from host only).
  • Provides support for 1st party DMA access to the host

Serial ATA drives and motherboards should begin to appear in 2002.  Motherboards will probably include old ATA and serial interfaces for a while to accommodate older drives.  Serial ATA should be cost-competitive with equivalent parallel ATA solution at introduction.

Serial ATA Disk Drive Specification

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