6. Serial ATA Questions & Answers
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LaCie d2 Hard Drive Serial ATA
User’s Manual
6. Serial ATA Questions & Answers
What is Serial ATA?
The Serial Advanced Technology Attachment (ATA) is the evolutionary successor to the Parallel ATA/ IDE (Integrated Drive
Electronics) interface, which has been in use for the last twenty years to connect peripheral devices to the computer. The
Parallel ATA standard can deliver data at a maximum of 133MB/s, while Serial ATA provides for a data throughput of
150MB/s with the initial release, and specification developers are planning increased speeds over the next several years.
Serial ATA removes the performance bottleneck of the Parallel ATA specification, and follows a clearly defined road-map to
greater and greater data transfer rates and feature improvements.
Deriving its name from the way that it transmits signals, in a single stream, or serially,
Serial ATA operates in a point-to-point topology. This connectivity methodology delivers the entire available interface
bandwidth to each device, allowing each device to operate at its maximum throughput, and provides direct communication
between the device and the system at any time, reducing arbitration delays associated with shared bus topologies.
What are the features and benefits of Serial ATA?
The Serial ATA specification provides several key advancements that will help spur widespread implementation:
• Performance: Serial ATA is a point-to-point topology, and does not have to share the bus, instead dedicating full bandwidth
to the device. These dedicated links make creating a Serial ATA RAID array quick and relatively inexpensive to implement.
• Easy installation and configuration: There are no device IDs, termination or master/slave conflicts, and the standard
supports hot-plug connectivity. Drives can be added, upgraded or removed without having to power down the whole system.
• Improved reliability: Serial ATA also uses 32-bit cyclic redundancy checking (CRC) on all transfers to ensure correct data
transmissions. Due to this CRC capability, Serial ATA performs protection and recovery features at multiple levels: PHY layer,
link layer and transport and software layers.
• Command optimization: Serial ATA utilizes Native Command Queing (NCQ) and first party direct memory access (DMA)
to intelligently order commands in an internal queue within the drive, without having to involve the host CPU. Judging its own
drive head’s angular and rotational position, the drive selects a data transfer from the queue that will minimize both its seek
and rotational latencies.
• Simplified structure: Serial ATA utilizes a more efficient signaling voltage (250mV vs. 5V for Parallel ATA), and much
smaller, thinner and compact cables and connectors. Due to the simplified cabling (the reduction in the number of pins and
wires), the number of fault possibilities decreases.
