About Serial ATA

What Is Serial ATA?
Serial ATA (Advanced Technology Architecture) is an interface that is used to connect hard drives and other peripherals to a PC. It is the next-generation replacement for the Parallel ATA (PATA) physical storage interface and will be used to connect storage devices such as hard disc drives, DVDs and CD-RWs to the motherboard.

Why has Serial ATA been developed?
The Advanced Technology Attachment (ATA) interface (previously called Integrated Drive Electronics (IDE)) has existed in substantially the same form since 1989. As PC processor performance has increased, so have the read/write data rates of hard disk drive (HDD) heads and media. This disk rate is projected to exceed today's 100 MB/s interface bandwidth by 2004. Parallel ATA data transfer bandwidth is nearing its limit, and therefore becoming a performance bottleneck.  

Serial ATA has been developed to eliminate this bottleneck by initially offering 150 MB/s and in the future it will provide significant headroom for future improvements. In other words, Serial ATA is scalable and allows future enhancements to the computing platform. Serial ATA allows
the performance and growth to continue without adding costs and extra ordinary means to achieve the requirements.

How does Serial ATA compare to Ultra ATA-100?
Ultra ATA-100 was the latest-generation Parallel ATA interface. With its maximum burst data transfer rate of 100 MB/sec, it superseded the Ultra ATA-66 interface. Before the industry completes its final transition to Serial ATA, Ultra ATA-100 is the last Parallel ATA interface.

Why should I migrate from Parallel ATA to Serial ATA?

• Parallel ATA’s 5-Volt signaling requirement limits other system performance improvements.
   
  Since the industry continues to reduce chip core voltages, Parallel ATA's 5-volt signaling requirement is increasingly difficult to meet. Parallel ATA has 26, 5-volt signals per ATA channel, requiring the use of large physical chip pads to accommodate the high pin count.  The large pads will ultimately dominate the chip as chip sizes are reduced.
   

• With the Parallel ATA interface, the 18-inch cable length limitation can be a serious issue.
   
  The limited cable length complicates peripheral expansion choices, making some internal drive configurations impossible to implement. Of course, this depends on PC chassis size and the design and location of internal media bays.  
   

• The wide, flat ribbon cables of the Parallel ATA bus are difficult to route. And, their shape and bulk can restrict air flow and create hot spots inside the chassis.
   

• With Parallel ATA, data robustness has been a long-standing issue. During its early development, no form of data checking was designed into the Parallel ATA interface.
    

• Motherboard and system manufacturers are behind the migration. Most new motherboards being produced currently utilize the Serial ATA interface and more will continue to adopt the technology. Serial ATA storage devices are now beginning to reach the market, with more slated for introduction throughout 2003.

What are the actual benefits I will see from Serial ATA?

• The Serial ATA interface is faster. Serial ATA delivers data transfer rates beginning with 1.5 Gbps, and scalable to 2x, 4x and beyond.
   

• Serial ATA reduces system voltage requirements. Serial ATA's low-voltage requirement (500 mill volts [mV] peak-to-peak) effectively alleviates the increasingly difficult-to accommodate 5-volt signaling requirement. This requirement hampers the current Parallel ATA interface.
   

• The Serial ATA architecture replaces the wide Parallel ATA ribbon cable with a thin, flexible cable that can be up to 1 meter in length. The serial cable is smaller and easier to route inside the chassis. The small-diameter cable can help improve air flow inside the PC system chassis and facilitates future designs of smaller PC systems. The lower pin count of the smaller Serial ATA connector eliminates the need for the large and cumbersome 40-pin connectors required by Parallel ATA.
   

• Serial ATA improves robustness of data. Serial ATA offers more thorough error checking and error correcting capabilities than was available with Parallel ATA. The end-to-end integrity of transferred commands and data can be guaranteed across the serial bus.
   

• Serial ATA is a drop-in solution that is 100% compatible with your existent ATA software drivers and runs on standard operating systems without modification.
   

• Serial ATA provides backward compatibility for legacy Parallel ATA and ATAPI devices.  This can be accomplished by two methods:

1. First, you can use chip sets that support Parallel ATA devices in conjunction with discrete components that support Serial ATA storage devices. These discrete components are now available. An integrated chip set, which supports a mix of serial and parallel channels is also available.
    

2. Second, you can use the Bare-Bone Serial ATA to Parallel ATA adapter which adapts parallel devices to a serial controller and adapts serial devices to a parallel controller.

• Configuration of Serial ATA storage devices is much simpler, with many of today's requirements for jumpers and settings no longer needed.

Are there differences In Serial ATA Solutions?
There are two main methods for establishing the Serial ATA interface on the disc drives and hosts, "native" and "bridge."

1. "Native" solutions, such as the Bare-Bone Serial ATA to Parallel ATA Adapter, allow maximum throughput at Serial ATA data transfer rates. These solutions bypass the legacy Task File reads and writes and the limitation of 133MB/sec for Ultra DMA Mode 6 transfers to enable the maximum 150MB/sec transfer rate for first-generation Serial ATA storage devices.
    

2. “Bridge” solutions enable the adoption of a parallel device to the Serial ATA interface. Because the Serial ATA information flow occurs at 1.5Gbps, it is not always possible for the Link state machines to keep up when using a bridge device. The link layers on a bridged system must incorporate buffering to allow for throttling the interface if one side gets behind.