Serial ATA technology promises to replace today's parallel technology for connecting internal computer drives. Summarily, This equates to the following improvements:
More bandwidth (exceeding 3GB/s).
Longer and thinner connection cables.
Lower power consumption.
Backwards compatibility with parallel technology.
The following is a general overview of the Serial ATA standard obtained at serialata.org.
Serial ATA: The Next Generation Internal Storage Interconnect
Provides Long-Term Solution for Higher Performance and Easier, More
Flexible System Design
A group of computer industry leaders have developed a next generation ATA specification that is
intended to provide scalable performance for the next decade. Serial ATA is designed to be 100%
software compatible with today’s ATA, but has a much lower pin count, enabling thinner, more
flexible cables. APT, Dell, IBM, Intel, Maxtor, and Seagate are jointly leading this initiative, with
broad industry support from the 74 companies that make up the Serial ATA Working Group.
Last year at the Intel Developer Forum (IDF) Spring 2000, the formation of the Serial ATA
Working Group was announced. Since then, tremendous progress has been made in the
development of the technology. The final Serial ATA 1.0 specification was released on August
29, 2001 at the IDF Fall 2001, with an initial speed of 1.5Gb/s (Gigabits per second). Product
development is in full swing, with several industry vendors currently targeting their products to be
available in the first half of 2002. Also, several public Serial ATA demonstrations have been
shown at recent events such as the Intel Developer Forum. It is anticipated that Serial ATA will
allow the performance of internal storage devices to continue to increase for generations to come.
Overview of the ATA Interconnect
Originally introduced in the 1980s, the parallel ATA interconnect has been the dominant internal
storage interconnect for desktop and mobile computers. It has been used to connect storage
devices such as hard drives, DVD and CD drives, and others to the motherboard. Parallel ATA’s
relative simplicity, high performance, and low cost has enabled it to attain the cost/performance
ratio that is essential in the mainstream desktop and portable PC market.
Parallel ATA’s longevity can be attributed to frequent improvements in the interconnect’s speed
and overall performance, allowing it to stay ahead of the performance needs of the industry’s
fastest hard drives. For example, ATA’s data transfer rate has increased steadily from less than
3 Megabytes per second (MB/s) to its current maximum burst data transfer rate of up to 100MB/s.
Other evolutionary improvements have helped it keep up with overall system requirements,
including enhanced data modes such as Ultra DMA, and ATAPI for DVD and CD drive support.
However, parallel ATA has a number of limitations that are exhausting its ability to continue
increasing performance. Some of these limitations are as follows:
Serial ATA: The Long-Term Solution
5-volt signaling requirement: In the near future, integrated circuits manufactured on the
leading manufacturing processes will not be able to efficiently support 5-volt signaling
High pin count: Parallel ATA, with its 26 signals, requires a 40-pin connector and uses
an unwieldy 80-pin ribbon cable to route inside the chassis. This high pin count is
problematic for chip design and makes it difficult to route traces on a motherboard. The
wide ribbon cable impedes airflow in the chassis, making thermal design more difficult.
These issues become especially acute in notebooks and small form factor desktops,
servers, and networked storage.
Serial ATA is intended to replace today’s parallel ATA. It is designed to address many of the
limitations of parallel ATA, while maintaining 100% software compatibility. This will significantly
ease the transition to Serial ATA, as no changes in today’s drivers and operating systems should
be required. In fact, demonstrations have already shown prototype hardware running on several
Windows and Linux operating systems.
Serial ATA enables the industry to move to the lower voltage and lower pin count required for
efficient integration in future chipsets and other integrated silicon components. The lower pin
count also benefits the system design by making it easier to route traces around a motherboard.
It enables a thinner, more flexible cable that improves airflow and therefore facilitates the
development of better thermal design and smaller form factor systems. In addition, the new
connector is more reliable, which should improve the end user upgrade experience.
Parallel ATA cannot scale to support several more speed doublings, and is nearing its
performance capacity. By contrast, Serial ATA’s roadmap starts at 1.5 gigabits per second
(equivalent to a data rate of 150 MB/s) and migrates to 3.0 gigabits per second (300 MB/s), then
to 6.0 gigabits per second (600 MB/s). This roadmap supports up to 10 years of storage
evolution, based on historical trends.
Parallel ATA disk drives are limited by their signal and power connectors to cable-attached
applications. The Serial ATA connector, which can be blind-mated and hot-plugged, enables
Serial ATA disk drives to be used in both cable and backplane attached applications. This
capability is expected to accelerate the acceptance in enterprise market segments.
As with parallel ATA, Serial ATA is expected to be integrated into industry chipsets. Once these
chipsets reach high volume, it is expected that Serial ATA will be about the same cost as parallel
ATA is today at a system level. Because of this, Serial ATA is expected to eventually completely
replace parallel ATA, which is already ubiquitous in PCs today. Also like today’s ATA, Serial ATA
will satisfy the storage interface needs of desktop and mobile PCs, as well as entry servers and
networked storage solutions. Over time, Serial ATA is expected to be deployed in enterprise
segments that parallel ATA has not reached before.
Serial ATA is the most suitable technology to continue the success of parallel ATA into the future.
Just like today’s ATA, it is dedicated to internal storage and its protocol has been optimized to
provide the highest performance at the lowest cost. With integration into industry chipsets, it can
achieve a similar cost structure as today’s ATA, which is an absolute requirement especially for
low-cost desktop PCs. Also, its 100% software compatibility with today’s ATA will ease the
industry transition to Serial ATA. Other high-speed serial interconnects such as USB 2.0 and
1394 are useful for external storage connections, but as more general-purpose interconnects they
do not achieve the performance levels nor relative simplicity that Serial ATA can provide.
The Serial ATA specification now provides a stable platform for product development and
deployment. Serial ATA delivers the best long-term storage interface solution, addressing the
shortcomings of parallel ATA while delivering scalable performance to support an interface
roadmap spanning at least 10 years. It enables the industry to move to the lower signaling
voltages and reduced pin counts required for efficient integration in future integrated silicon
components. At the same time, it dramatically improves the cable and connector plant, improving
both manufacturability and ease of use. The first products offering Serial ATA are expected in the
marketplace in the first half of 2002.
For more information, see the Serial ATA Working Group web site at www.serialata.org.