Comment Re:128 or 256 GT/s in each direction? (Score 1) 17
It's not a contradiction, but it's an error. Perhaps the author did not properly understand the distinction between bits/sec and Transfer/sec.
Up to gen 5, gen N meant roughly 2^N transfer per second.* It was regular NRZ encoding so GT/s ~= Gb/s.
In Gen6, they went to PAM4, so 2 bits per transfer. Gen6 is still 32GT/s, but 64Gb/s per lane.
16 lanes of Gen6 is128GB/s (B = Byte).
In Gen7, they went back to increasing the transfer rate, and of course kept the PAM4 encoding. 64GT/s @2b/T = 128Gb/s, x16 lanes is 256GB/s.
*Up to Gen2, it was 8b/10b encoding so they were 2.5GT/s (for effective 2Gb/s) and 5GT/s (for effective 4Gb/s) for the first 2 generations.
After that, encoding changed to 64b/65b so the GT/s ~= Gb/s.
FLIT encoding is now required (or maybe it was required in Gen6. Too lazy to look up) I think this increases efficiency by further reducing encoding overhead.