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LaCie Biggest S2S
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Tech Tips
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What is Serial ATA II?
The Serial Advanced Technology Attachment (ATA)
II marks the latest rung on the evolutionary ladder of
SATA technology. SATA II can deliver data at 300MB/
s, twice as fast as its SATA predecessor and more than
twice as fast as the Parallel ATA/ IDE (Integrated Drive
Electronics) interface, which has long been used to con-
nect peripheral devices to the computer. Initial Serial
ATA technology removed 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 sig-
nals, in a single stream, or serially, Serial ATA operates
in a point-to-point topology. This connectivity method-
ology delivers the entire available interface bandwidth
to each device, allowing each device to operate at its
maximum throughput, and provides direct communi-
cation between the device and the system at any time,
reducing arbitration delays associated with shared bus
topologies.
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What are the key differences between Serial ATA
and Serial ATA II technology?
SATA I requires that parallel ATA drives be config-
ured as master and slave and daisy-chained from each
controller. Not so with SATA II. In addition to deliver-
ing data at twice the speed of SATA, SATA II also fea-
tures port-multiplier options allowing for many drives
to be connected to a SATA II controller.
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What are the features and benefits of Serial ATA
and Serial ATA II?
The Serial ATA specification provides several key
features that will help spur widespread implementa-
tion:
Performance: Serial ATA is a point-to-point topol-
ogy, and does not have to share the bus, instead dedi-
cating 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 de-
vice 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 cy-
clic redundancy checking (CRC) on all transfers to
ensure correct data transmissions. Due to this CRC
capability, Serial ATA performs protection and re-
covery features at multiple levels: PHY layer, link
layer and transport and software layers.
Command optimization: Serial ATA utilizes Na-
tive Command Queing (NCQ) and first party direct
memory access (DMA) to intelligently order com-
mands in an internal queue within the drive, with-
out 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 mini-
mize both its seek and rotational latencies.
Simplified structure: Serial ATA utilizes a more ef-
ficient 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 num-
ber of fault possibilities decreases.
Seamless integration: Serial ATA maintains register
and software compatibility with Parallel ATA, and
should be transparent to both the BIOS and oper-
ating system. Simply add more Serial ATA links to
increase the number of connectivity points in your
system.
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8.3. Serial ATA II Questions and Answers