in the Intel 7 Series / C216 Chipset Family Platform Controller Hub
there's only words
"PCI Express Root Ports 1-4 or Ports 5-8 can be independently configured as four x1s,
two x2s, one and two x2 x1s, or one x4 port widths. The port configuration is set by
soft straps in the Flash Descriptor."
the text says only about four Pci-Ex lines.
document 7-series chipset-pch-datasheet.pdf says nothing about support "bifurcation"
but the Core i7 processor supports 16 Pci-Ex lines
the Intel Core i7-3770 supports "bifurcation" (page 68 of document)
in the specifications of the motherboard GIGABYTE GA-Z77N-WIFI said
1 x PCI Express x16 slot, running at x16 (The PCIEX16 slot conforms to PCI Express 3.0 standard.) Whether PCI Express 3.0 is supported depends on the CPU and graphics card compatibility.
http://www.gigabyte.us/products/product-page.aspx?pid=4337#sp
motherboard GIGABYTE GA-Z77N-WIFI works with Core i7-3770
http://www.gigabyte.us/support-downloads/cpu-support-popup.aspx?pid=4337
but there is no indication of support "bifurcation" because there is no such information in documents from Intel. such answer was given by support team GIGABYTE !