Ultra ATA/66

The Newest IDE Interface...

Ultra ATA/66 is the newest generation Ultra ATA IDE interface that doubles the current burst data transfer rate to 66.6 MB per second. The high-speed interface allows host computers to send and retrieve data faster and removes bottlenecks associated with today's system performance.

Ultra ATA/66 interface benefits include:

A low cost extension to the Ultra ATA/33 IDE interface, Ultra ATA/66 can go farther in removing bottlenecks associated with data transfers, especially during sequential operations. The new interface offers heightened data integrity to the EIDE interface through use of a 40-pin 80-conductor cable which reduces crosstalk and improves signal integrity by providing 40 additional ground lines between the 40-pin IDE signal and ground lines. This connector is plug-compatible with existing 40-pin headers, and the increased cost for the cable should be minimal.

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Ultra ATA/66 hard drives are 100 percent backwards compatible with both Ultra ATA/33 and DMA, and with existing EIDE/IDE hard drives, CD-ROM drives and host systems.

Ultra ATA/66 offers the fastest ATA/IDE hard drive data transfer protocol for moving data between the hard drive buffer and the system memory. The previous interface, Ultra ATA/33, had a maximum burst transfer rate of 33.3 MB per second. Prior to Ultra ATA/33 was multi-word DMA Mode 2 with a maximum burst transfer rate of 16.6 MB/s. Ultra ATA/66 doubles Ultra ATA/33’s maximum burst rate and quadruples multi-word DMA’s maximum burst rate to 66.6 MB/s.

By increasing the burst transfer rates of IDE drives, Ultra ATA/66 brings the effective transfer rate of the system’s bus and a drive’s internal data rate into a much closer balance. Ultra ATA/66 allows system designers to provide greater system throughput, particularly for long sequential transfers required by multimedia applications. It is a known fact that host data transfer rates must exceed media data transfer rates or else performance is reduced because of additional revolutions due to buffer full/empty conditions on reads/writes.

New hard drive technologies continue to offer expansions in disk capacity and higher rotational speeds, the hard drive’s internal disk rates also continue to increase. The transfer of large files written sequentially on the hard drive is particularly affected by the transfer rate. During sequential reads, the hard drive, because of its fast internal data rate, can fill its buffer faster than the host can read and empty it when using the Ultra ATA/33 or older multi-word DMA interfaces. Performance bottlenecks usually result in this interface between the host and the hard drive. Improving this connection to keep up with internal data rate improvements is what Ultra ATA/66 is all about.

Ultra ATA/66 Further Improves Transferred Data Integrity
Ultra ATA/33 introduced Cyclical Redundancy Check technology, a feature that provides data protection verification. Ultra ATA/66 uses the same process. The CRC is calculated on a per-burst basis by both the host and the hard drive, and is stored in their respective CRC registers. At the end of each burst, the host sends the contents of its CRC register to the hard drive, which then compares it against its own register's contents. If the hard drive reports errors to the host, then the host retries the command containing the CRC error.

Data transfer was performed on the ATA bus up through multi-word DMA Mode 2 (16.6 MB/s) by sending the data in synchronous strobe mode but only on the positive transition of the strobe signal. The Ultra ATA/33 extension was key in achieving the use of both the positive and negative transitions of the strobe signal, effectively doubling the available transition frequency without actually increasing the frequency of the strobe. The result was to double the burst transfer rate. By having the hard drive as the source of both the strobe and the data during a read, Ultra ATA/33 eliminated both propagation and data turnaround delays. The elimination of these delays improved the timing margins. Ultra ATA/66 retains the same strobe frequency but doubles the Ultra DMA/33 burst transfer rate, this time by reducing setup times. Timing signals are made twice as fast. However, the new 80-conductor cable is needed to ensure the data's integrity. The 40-conductor/40-pin interface cable of the earlier Ultra ATA/33 interfaces can't handle the shorter cycle times for a 44.4 MB/s or 66.6 MB/s burst rate. The 80-conductor cable retains the same connector configuration as the standard 40-pin interface cable but has ground lines (which act as shields) interleaved between all signal lines.

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