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The past few years have seen enormous progress in the development of hard disks, controllers, and video cards. The
older ISA bus architecture restricts the power and performance of PC-based digital video editing. The narrower
bandwidth (data throughput) meant higher compression rates, which limited quality. Only professional systems with
their own onboard hard-disk controllers could bypass the bus architecture and achieve professional image quality and
performance at low compression rates.
The new PCI bus architecture supports bandwidths of up to 132 MB/s. This means that we can now transfer enormous
amounts of digital video data directly over the PCI bus. The technology largely eliminates the need for hard disk
controllers on video cards, and at the same time makes it easier and less expensive to integrate the board into the system. Not all PCI boards are created equal. This product is a true Bus Masters, and the new generation of PCI motherboards
supports this technology. The result is exceptional PCI bus performance.
Up to now, most PCI-based multimedia and video cards have been "slaves." Unlike master cards, slave cards use the
CPU even for comparatively "dumb" operations: they make demands on the CPU every time they access memory or
copy data. For example, a data rate of 4 MB/s (6:1 compression ratio) already loads the CPU to 60% (average). The
result is that the CPU becomes a bottleneck and makes the PCI bus' bandwidth unusable. Because the PCI slave must
wait, it makes for a sluggish system until the CPU releases the bus. Only then can data pass through the bus. So actual
performance depends on the available CPU capacity and the card's interaction with the rest of the system.
In contrast, this unit uses Bus Master: it controls access to the data bus itself. Bus Master cards can make data
available, and, at the same time, direct a slave (for example, a hard-disk controller) to retrieve data. As a Bus Master,
this unit assumes the entire task of copying video. It can write directly to main memory (RAM), and read from it (DMA),
freeing the CPU for many other important tasks.
it also has a video-RAM (FIFO) that collects data and sends a "packet" to the entire bandwidth in burst mode. This
packs the bus for only a very short time, yet takes full advantage of the bandwidth. The bus is then released
immediately for other tasks. In short, Bus Master cards significantly increase the overall system performance by
supporting high data transfer rates.
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DIGITAL VIDEO & PCI