LaCie Two Big eSATA & USB
User Manual
page
6.3. Serial ATA II Questions and Answers
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 connect
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
signals, in a single stream, or serially, Serial ATA
operates in a point-topoint 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 key differences between
Serial ATA and Serial ATA II technology?
Serial ATA (SATA) II allows twice the transfer
speed of Serial ATA and can support what’s called a port
multiplier. With a port multiplier, the controller (the
PCI-X card) can communicate with multiple SATA
drives from one host channel (this process is often
called “Daisy Chaining”). One Serial ATA II channel
from the PCI-X card can communicate with up to two
disks in the Two Big.
■
■
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 implementation:
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-
■
❖
❖
❖
❖
❖
Tech Tips
