Seagate Enters the World of Ultra ATA Beyond ATA Working with two other high-tech companies, Seagate has launched the Ultra ATA interface in its Medalist® 1722 and Medalist® 2122 drives. This interface enables users to experience data-transfer rates far beyond the current interface of choice for desktop and portable computer operators: Fast ATA-2. Why Ultra ATA? Today's desktop computer users are downloading huge files from the Internet onto their hard drives, manipulating high-resolution photo images, using advanced sound capabilities, producing massive 3-D graphics and creating complex database files. Technology is pushing the demand for speed. As the amount of data streaming between the hard drive and the host grows, so does the need to keep increasing amounts of data moving along at top speed. Ultra ATA sets a new performance trend, boosting data-transfer rates up to 33.3 Mbytes per second—more than twice the speed of its predecessor, Fast ATA-2, which transfers data at up to 16.6 Mbytes per second. Ultra ATA Benefits Based on the Ultra DMA/33 technical specification, Ultra ATA was designed and developed by leading manufacturers in the computer industry: Intel, Quantum and Seagate to provide desktop and portable computer users with the hard disc drive performance gains required by today's advancements in technology. To ensure the best PC performance, PC system designers rely on innovations in hard drive performance such as Ultra ATA, which can improve throughput of the entire PC. Ultra ATA incorporates an error-detection mechanism that allows system retries for improved data integrity. If the built-in cyclical redundancy checking (CRC) data-verification system detects an error, the data-transfer operation will try again. With Ultra ATA, the CRC system protects data reads and data writes. Ultra ATA is completely backward-compatible with existing Fast ATA-2 (EIDE) systems and can be connected easily into legacy systems. Cables will continue to support the traditional 40-pin ATA signal without change. However, to get the benefits of Ultra ATA, the user's system must also support Ultra ATA. Ultra ATA supports multiple drives on a single cable and improved performance in transferring data stored in the drive's cache.| Ultra ATA provides a cost structure similar to its predecessor, Fast ATA-2. With up to twice the speed with no additional investment in equipment, training and procedures required, customers get more for their money. Developments in Interface Technology The hard disc drive interface is like a path through which user data travels between the PC and the hard drive. The original interface standard architecture (ISA)-dependent interface enabled the transfer of data at speeds ranging from about 4 Mbytes per second to 8 Mbytes per second. Then, interface protocols, such as programmed input/output (PIO) and direct memory access (DMA) modes, were developed to take advantage of the new local bus architectures that replaced ISA. Over time, improvements in the PIO and DMA interface protocols enabled data-transfer rates of 8.3 Mbytes per second to 13.3 Mbytes per second, up to the current Fast ATA-2 speed of 16.6 Mbytes per second. Figure 1 The trends in Figure 1 show that several hard drive components have improved as the ATA interface has evolved. In addition to speed, functionality has also improved. Hard drive performance, however, remains the attribute most commonly associated with the evolution of interfaces. Technical Information How Data Moves In ATA-2 and ATA-3, the host sends a clock pulse (or strobe) to regulate data transfers to and from the disc drive. This clock pulse consists of one pulse for each word of data. To move data, the initial leading (rising) edge of the strobe starts the data access, after which the rising edge of the pulse transfers data. A faster pulse means faster data transfer. As the pulse rate increases, however, the system becomes increasingly sensitive to signal interference (noise). To make the most of existing clock pulses, a new way of treating the existing signal was conceived. Both the rising and falling edges of the pulse signal are used to send and receive data. The same pulse provides two strobes (the rising and falling edges) without actually increasing the speed of the strobe. In fact, twice as much data is transferred within the same time period since both the rising and falling edge of the pulse are used. This approach is somewhat like sticking to the same bus schedule, but using double-decker buses to move twice as many people from one place to another. Asynchronous versus Synchronous Original ATA was based on transistor-transistor logic (TTL) bus interface technology, or asynchronous data transfer. The host initiated a data transfer, data was made available, and some time later, the data was collected by its receiver. Asynchronous data transfer is based on timings that allow for some leeway between activities and assumes that the data transfer occurs. However, asynchronous transfer is like passing a baton in a relay race to the next runner without looking. Synchronous data transfer, on the other hand, provides better timing margins by more closely managing the process of moving data. With synchronous data transfers, the sender of data also sends the strobe with the data. The transfer is no longer open loop; the drive now controls the strobe, data transfer and data recovery. The relationship of the strobe and the data is entirely determinate, and propagation times and access times are made irrelevant. In other words, the runner in a relay race now looks before passing the baton. Figure 2 compares Ultra ATA data movement to Fast ATA-2. The traditional, Fast ATA-2 method looks at the rising edge of the signal to indicate a pulse. Ultra ATA looks at the same pattern but can discern a pulse based on rising and falling edges of the signal. Figure 2 Figure 2 shows how the cycle time of Ultra ATA moves from 120 nsec to 60 nsec while the strobe frequency remains the same. Twice as much data can be moved in the same amount of time. This is how the Ultra ATA interface doubles throughput to 33.3 Mbytes per second. Half the cycle time provides twice the throughput. Data Reliability Data reliability is an important benefit of Ultra ATA, and the interface takes extra steps to protect user data. Figure 3 shows that a register exists in both the host side and drive side of the Ultra ATA connection. A cyclical redundancy check (CRC) value resides in these registers. Initially, the value of this register is set; subsequent data transfers use a calculated value. CRC is calculated on a per-burst basis using the CRC polynomial applied to the current value of the CRC register. The drive then compares CRC data from the host with its CRC calculation register. If the two values do not match, the drive latches and reports the error, at the end of the command, in data transfers to or from the disc drive. The data transmission can then be repeated, ensuring data reliability. Because all error checking is performed on the drive, not on the host, backward-compatibility is maintained. If the host detects an error, it flags the drive for confirmation and parity rebuild of the data.

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