About Serial ATA
- Lower Voltage - Parallel
ATA is based on TTL signaling, requiring integrated circuits to
tolerate input signals as high as 5 volts. Soon, integrated circuits
manufactured on the leading manufacturing processes will not be able to
efficiently support 5 volt signaling voltages. With the upcoming fine
lithographies, it will not be practical to support 5 volt signaling
tolerance. Serial ATA manages this by reducing signaling voltages to
approximately 250 millivolts (0.25 volt).
- Pin Efficiency - Currently, the parallel ATA
interface has 26 signal pins going into the interface chip. Serial ATA
uses only 4 signal pins, improving the pin efficiency and accommodating
a highly integrated chip implementation.
- Improved Cable and Connector Plant - The
current parallel ATA cable and connector are bulky, made up of 80
conductor ribbon cables and 40 pin header connectors. Instead, Serial
ATA uses a much smaller serial cable similar in appearance to modern
telephone cables. Eliminating a cable nest improves system airflow and
cooling, and offers greater freedom in chassis design. Serial ATA also
improves manufacturability and ease of use by allowing better connector
and cable design.
- Master-Slave Interaction - With today's
parallel ATA implementation, pairs of devices share a common cable in a
master-slave relationship, resulting in available bandwidth being
shared between the devices. Also, since devices on the cable interact,
they must be jointly qualified, resulting in substantial expansion of
the system integrators' qualification matrix in order to comprehend
possible combinations of devices. By contrast, Serial ATA is a
point-to-point interface where each device is directly connected to the
host via a dedicated link. Therefore, each device has the entire
interface bandwidth dedicated to it, and there is no interaction
between devices. As result, software can be streamlined, eliminating
the overhead associated with coordinating accesses between the master
and slave device sharing the same cable.
- Hot-Plug Opportunity - A benefit of Serial
ATA is that it provides the opportunity for devices to be hot-plugged
and inserted directly into receptacles, an approach that is not
directly supported by parallel ATA. Serial ATA includes all the
mechanical and electrical features necessary to allow devices to be
directly inserted into receptacles while the system is powered
(commonly referred to as "hot-plugged"), and the protocol ensures that
device discovery and initialization are handled.
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