Easing into PCI Bus

The reason 64 bit helps is that it improves the bandwidth of the PCI Bus. Bandwidth, normally expressed in MB per second, is basically a measure of the amount of data that can be pushed through something at one time.If you ever have sat in your car looking at the back bumper of another car during rush hour then you probably have a good idea of what's going on in the modern PCI Bus. You've got too many cars (data) going through too narrow and too slow a road (PCI Bus) at one time.
Bandwidth
PCI Express in all its flavors: 1x, 2x, 4x, 8x, 16x and 32x all have much greater bandwidth than basic PCI.

Common Buses and their Max Bandwidth

PCI 132 MB/s AGP 8X 2,100 MB/s PCI Express 1x 250 [500]* MB/s PCI Express 2x 500 [1000]* MB/s PCI Express 4x 1000 [2000]* MB/s PCI Express 8x 2000 [4000]* MB/s PCI Express 16x 4000 [8000]* MB/s PCI Express 32x 8000 [16000]* MB/s USB 2.0 (Max Possible) 60 MB/s IDE (ATA100) 100 MB/s IDE (ATA133) 133 MB/s SATA 150 MB/s SATA II 300 MB/s Gigabit Ethernet 125 MB/s IEEE1394B [Firewire 800] ~100 MB/s*

Since PCI Express is a serial based technology, data can be sent over the bus in two directions at the same time. Normal PCI is Parallel, and as such all data goes in one direction around the loop. Each 1x lane in PCI Express can transmit in both directions immediately. In the table the first number is the bandwidth in one direction and the second number is the combined bandwidth in both directions. Also please note that in PCI Express bandwidth is not shared the same way as in PCI, so there is less congestion on the bus.