Seagate STM380215A Serial ATA - A Comparison with Ultra ATA Technology (57K, P
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- Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 1
as hard drives, optical drives, and removable magnetic media devices. Ultra ATA is an extension of the original parallel ATA interface introduced in the mid 1980's and maintains backward compatibility with all previous versions of this technology. The latest revision of the Ultra ATA specification - Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 2
Strobe Required Hold Time 4.8ns Required Setup Time 4.8ns Data 10.4ns Max Switching Time Figure 1 - Ultra DMA Burst Transfer Timing Serial ATA Bus Architecture Bus Design - In contrast to Ultra ATA's parallel bus design, Serial ATA uses a single signal path to transmit data serially, or bit - Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 3
to become critical roadblocks to further Ultra ATA speed increases. Serial ATA alleviates many of these problems by transitioning to a serial data -speed drivers, both common with parallel data busses. The instantaneous power draw is such that the decoupling capacitors for the device cannot supply - Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 4
the challenges in increasing the speed of the Ultra ATA specification further, a shift in design strategy is required. Serial ATA addresses this need by making the transition to a high-speed serial bus. To mitigate many of the design problems associated with high-speed single -ended and/or parallel - Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 5
Impedance Specifications / Support for Automatic Impedance Matching Since Serial ATA uses only 4 signal lines per channel, proper termination of all lines is less costly, both in design complexity and dollars. All devices are required to provide precision termination impedances. Support is also - Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 6
with previous ATA specifications, the 5V tolerance constraint is removed. Serial ATA - Beyond Better Signaling Characteristics... Connection Methodology Ultra ATA - Master/Slave Shared Bus Ultra ATA technology supports up to 2 drives per channel via a shared bus. Though the two attached devices are - Seagate STM380215A | Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 7
only data packets in Ultra ATA. Also, Serial ATA supports hot-swapping via hardware support and by design of the connector (variable length pads, minimal insertion force design, and a specified location on device backing plates). With the proper software drivers Serial ATA devices may be hot-plugged
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Serial ATA : A Comparison with Ultra ATA Technology
- 1 -
Serial ATA
A Comparison with Ultra ATA Technology
In past years, increasing hard disk transfer rates have forced the ATA interface specification to be
continuously updated to avoid becoming the limiting factor in disk I/O performance.
As consumers
embrace new usage models such as digital video creation and editing, digital audio storage and
playback, file sharing over high-speed networks, and other data intensive applications, demands on
hard drive throughput are expected to increase even further.
To keep pace, the storage interconnect
must be developed beyond existing Ultra ATA technology.
The new approach is Serial ATA, a serial
implementation of the parallel Ultra ATA interface.
With this paradigm shift in I/O design, the
roadmap of ATA will be extended beyond the theoretical limits of the Ultra ATA bus.
The purpose of this document is to educate the reader on the technical differences between Ultra
ATA and Serial ATA technology, and to provide explanation for the transition from a parallel to serial
bus architecture.
The key design points of each technology will be described and compared, followed
by an overview of the system level and end-user advantages of Serial ATA technology.
The ATA
protocol itself will not be discussed, as in this sense there is no difference between the technologies.
Serial ATA is software compatible with the ATA interface and thus will appear to the OS as a standard
ATA device.
Note that it is assumed the reader has an understanding of electrical engineering design
principles; the paper is intended primarily for OEMs, system designers, and product manufacturers who
are considering adding Serial ATA capability to their designs.
Technology Introduction
Ultra ATA is the primary internal storage interconnect for the desktop, connecting the host system
to peripherals such as hard drives, optical drives, and removable magnetic media devices.
Ultra ATA is
an extension of the original parallel ATA interface introduced in the mid 1980’s and maintains
backward compatibility with all previous versions of this technology.
The latest revision of the Ultra
ATA specification accepted by the ANSI supported INCITS T13 committee, the governing body for
ATA specifications, is ATA/ATAPI-6, which supports up to 100Mbyte/sec data transfers.
Development of the ATA/ATAPI-7 specification, an update of the parallel bus architecture that
provides up to 133Mbytes/sec, is currently being finalized. (www.t13.org)
Serial ATA is the next -generation internal storage interconnect designed to replace Ultra ATA
technology.
Serial ATA is the proactive evolution of the ATA interface from a parallel bus to a serial
bus architecture.
This architecture overcomes the electrical constraints that are increasing the difficulty
of continued speed enhancements for the classic parallel ATA bus.
Serial ATA will be introduced at
150Mbytes/sec, with a roadmap already planned to 600Mbytes/sec, supporting up to 10 years of
storage evolution based on historical trends.
Though Serial ATA will not be able to directly interface
with legacy Ultra ATA hardware, it is fully compliant with the ATA protocol and thus is software
compatible.
(www.SerialATA.org)
Parallel vs. Serial Bus Architecture Overview
Ultra ATA Bus Architecture
Bus Design –
The latest revision of the ATA specification, ATA/ATAPI-6 where Ultra ATA 100 is
defined, maintains backward compatibility with all previous ATA revisions, using the standard 16-bit
wide parallel data bus and 16 control signals across a 40-pin connector.
Bandwidth –
To understand the 100Mbytes/sec throughput, several factors must be considered.
With
a 16-bit data bus, two bytes are transmitted per bus transaction.
Thus to achieve a throughput of 100