That would be x16, PCIe is rated in the number of data paths. The most I've heard of any chipset potentially supporting is 32 data paths, that would be 2 x16 slots and no other slots! That's why companies are planning boards with 2 x16 slots operating in x8 mode, with 1/2 the throughput.
<font color=blue>Only a place as big as the internet could be home to a hero as big as Crashman!</font color=blue>
<font color=red>Only a place as big as the internet could be home to an ego as large as Crashman's!</font color=red>