In 10GBASE-R specification, Gearbox is defined to take care the data width adaptation between PCS & PMA. For example, after the 64b66b encoding, the PCS data width will become 66bits.

The gearbox will adapt the 66-bit datawidth to whatever data width that PMA is support.

May i know if we can have a PMA with serializer factor of 66. Does that mean Gearbox is not necassary or not needed in this case?