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SATA vs. PATA: the reality of Serial and Parallel ATA - Serial ATA

submitted on January 21, 2011 by psplove in "Products / Gadgets"
Examining Serial ATA's (SATA) comprehensive set of features illustrates how SATA addresses the shortcomings of Parallel ATA and the reasons for SATA as an ideal choice for deployment in enterprise-level and external RAID subsystems.

Hot-Plug Capability

Parallel ATA is handicapped by its inability to support hot-plug drives. Any Parallel ATA-based RAID solution requires the host bus into which the degraded array's RAID controller is plugged to be powered off before the failed drive can be replaced. The alternative is to continue using the degraded array that offers reduced throughput capability. Clearly, neither option is acceptable in an enterprise-level environment where 24x7 availability and high performance are important requirements. It is easy to see why SCSI and Fibre Channel that support hot-plug drives have not yielded any ground to Parallel ATA in the enterprise space in spite of ATA's cost advantage. With its support for hot-plug drives, SATA remedies this deficiency.

Decreased Width and Increased Length of Cables

Parallel ATA's ATA/ATAPI-4 standard improved signal integrity by introducing the 80-conductor cable with 40 conductive elements serving as grounds to reduce cross talk between adjacent signal lines. Though the increase in the number of conductive elements did not increase cable width over the existing 40conductor cables due to the use of thinner gauge wires, the width of these cables nevertheless impeded airflow necessary to cool a server and constrained chassis design. Furthermore, Parallel ATA continued to limit cable length to 18 inches that prevented efficient routing of its cables within chassis to reduce clutter and improve accessibility to components in the system.

SATA addresses the limitations of Parallel ATA by more than doubling cable length to 1 meter and using data cables comprised of only seven conductors--a pair of differential signal lines for transmitting and another pair for receiving, and a ground between and at each end of the transmission and reception pairs. These thin, flexible cables (with connectors only 8mm wide) can be conveniently routed to multiple drives with a very small footprint, albeit with some constraints on its bend radius. This feature is highly attractive to servers using internal RAID with high drive density.


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