The difference is very much physical, and 64-bit 33 MHz and 66 MHz PCI slots are not new. They are, however, not usually found in consumer boards, which is probably why you're not familiar with them, ...
Reducing the manufacturing costs by not providing for a slot which is gradually being replaced by PCI-E, PCI-X, and USB. PCI first came out in 1992. Both my PCI slots are unused. Some time ago, I had ...
Specifications for two new interconnect technologies were released yesterday by the Peripheral Component Interconnect-Special Interest Group (PCI-SIG), the group said in a press release (download PDF) ...