Seagate ST3500630A Serial ATA - A Comparison with Ultra ATA Technology (57K, P - Page 7

Serial ATA - Enhanced Reliability, Hot-Swap Support, First Party DMA Serial ATA adds 32-bit CRC error correction for all bits transmitted, as opposed to 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 internal to the box or blind-mated to a backplane or device bay. Serial ATA also provides built in support for first-party DMA, removing bottlenecks associated with on-board DMA controllers. Conclusions The intent of this document was to explain the transition to a new internal storage I/O bus design, and to illustrate the benefits of this transition. The paper described several electrical design challenges that complicate further speed increases to the Ultra ATA interface and provided explanation of how Serial ATA overcomes these issues. Next discussed were benefits of Serial ATA technology from the serial bus architecture, added features, and improved design. Serial ATA Achieves and Surpasses Bandwidth of Parallel Ultra ATA through Design Enhancements • Differential signaling allows rejection of crosstalk and ground-bounce as common-mode noise • Embedded clocking provides advantages of source-synchronous clocking without problems related to clock-skew from poor strobe signal integrity and mismatched trace lengths • More controlled cable design, allowing longer cables • Serial ATA connector properly deigned to reduce crosstalk, a major issue with the legacy Ultra ATA connector • Automatic impedance matching greatly reduces ringing and thus settling time • Less complexity and less board space required for trace routing • Low voltage signaling (as low as 0.5V max voltage) allows for compatibility with future design processes • Serial ATA bus architecture enhancements allow for an initial speed of 150Mbytes/sec, with a planned roadmap up to 600Mbytes/sec Serial ATA Offers Advantages over Ultra ATA Technology • Point to point connection topology ensures dedicated 150Mbytes/sec to each device • Thinner, longer cables for easier routing • Fewer interface signals require less board space and allow for simpler routing • Better connector design for easier installation and better device reliability • CRC error checking on all data and control information • Hot-swap capability • First-party DMA support References 1. "Serial ATA: High Speed Serialized AT Attachment Revision 1.0", Serial ATA Working Group 2. "Information Technology: AT Attachment with Packet Interface - 6 Rev. 3b", T13 Committee 3. Johnson, Howard - "High-Speed Digital Design: A Handbook of Black Magic" - Prentice Hall, 1993 Serial ATA : A Comparison with Ultra ATA Technology - 7 -