PCI Express
History and revisions

PCI Express version
Introduced
Line code
Transfer rate
Throughput
Throughput
Throughput
Throughput
Throughput
PCI Express version
Introduced
Line code
Transfer rate
×1
×2
×4
×8
×16
1.0
2003
8b/10b
2.5 GT/s
250 MB/s
0.50 GB/s
1.0 GB/s
2.0 GB/s
4.0 GB/s
2.0
2007
8b/10b
5.0 GT/s
500 MB/s
1.0 GB/s
2.0 GB/s
4.0 GB/s
8.0 GB/s
3.0
2010
128b/130b
8.0 GT/s
984.6 MB/s
1.97 GB/s
3.94 GB/s
7.88 GB/s
15.8 GB/s
4.0
2017
128b/130b
16.0 GT/s
1969 MB/s
3.94 GB/s
7.88 GB/s
15.75 GB/s
31.5 GB/s
5.0
expected in Q1 2019
128b/130b
32.0 GT/s
3938 MB/s
7.88 GB/s
15.75 GB/s
31.51 GB/s
63.0 GB/s

Question: How does PCI Express 3.0 line code different from the 2.0 version? 
Answer: PCI Express 3.0 upgrades the encoding scheme to 128b/130b from the previous 8b/10b encoding.