Seagate ST3500630A Serial ATA - A Comparison with Ultra ATA Technology (57K, P

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Serial ATA : A Comparison with Ultra ATA Technology

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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