Seagate ST3500630A Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 1
Seagate ST3500630A - Barracuda 500 GB Hard Drive Manual
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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 Serial ATA : A Comparison with Ultra ATA Technology - 1 -