Compared to the progress made every year in other
areas of computer technology such as processors and video cards,
computer I/O system technology would seem to be standing still… in fact it is.
Since the introduction of the original PCI bus back in the early 90’s, very
little has changed in the way that data is handled inside your
Hard drives, peripherals, LAN cards,
sound cards, USB, and firewire all pass data through the same I/O system as your
first 486 PC; the PCI bus running at 33mhz and shifting 133MB/s of
data. As an example of recent technology, a Pentium 4 with DDR memory can shift
2.1GB/s across the memory bus. The 8x AGP bus can pass about 2.1GB/s of data a
second too. These are technologies developed essentially to get around the
limitations of the PCI.
An ATA 133 hard drive on an Ultra/133 IDE
controller card can theoretically overload the PCI bus all by itself, though
only in brief bursts. The sustained transfer rate for current drives is too low
to do this however. Now let’s think about RAID, SCSI and now Gigabit
Ethernet.... All of these data transfer technologies are trying to
pump information through that slim little 133MB/s parallel PCI bus.
This is the definition of a bottleneck.