The first PCI slot, sometimes called "conventional PCI," has a 32- or 64-bit data bus and runs at 33 MHz or 66 MHz clock speed. A maximum bandwidtyono teen pattih of 133 MB/s for 32-bit slots & up to 533 MB/s for 64-bit slots were made possible by this design. Restrictions & Antiquated Systems. Although these specifications were revolutionary when they were released, more recent technologies have surpassed them with much higher data transfer rates.