AXIOMTEK STX88810VEA, Руководство пользователя

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STX88810 STX Evaluation Platform Module Series User’s Manual
Ultra DMA/66/100 Reference 64
Background
Ultra ATA/100 is the latest ATA/IDE hard drive data transfer protocol
for moving data between the hard drive buffer and the system memory.
The previous interface was Ultra ATA/66, with a maximum burst
transfer rate of 66.6 MB/s. Prior to Ultra ATA/66 was Ultra ATA/33 with
a maximum burst transfer rate of 33.3 MB/s.
By increasing the burst transfer rates of IDE drives, Ultra ATA/100
brings the effective transfer rate of the system’s bus and a drive’s
internal data rate that much closer into balance. Ultra ATA/100 allows
system designers to provide greater system throughput, particularly for
long sequential transfers required by audio/visual applications.
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.
Host Data Rate Requirements
As you can see by the chart, the host data transfer rate doubles about
every three years. The chart indicates that Ultra ATA/100 will reach its
limits by 2000. The industry has supported host transfer data rates
doubling previously with:
z
DMA Mode 2 at 16.6 MB/s in 1994
z
Ultra ATA/33 at 33.3 MB/s in 1997
z
Ultra ATA/66 at 66.6 MB/s in 1999
z
Ultra ATA/100 at 100MB/s in 2000
With continued expansions in disk capacity and higher rotational
speeds, the hard drive’s internal disk rates also continue to increase.
The transfer of large files, often 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, may fill its buffer faster
than the host can empty it when using the Ultra ATA/66 or the older
multi-word DMA interfaces. Performance bottlenecks usually result in
this connection between the host and the hard drive. Improving the
interface to keep up with internal data rate improvements is exactly
what Ultra ATA/100 can achieve.
As previously mentioned, fast host data transfer rates help maintain
sequential media transfers, but they also accelerate cache hits. The