That's not to say that XENPAK wasn't a significant advance when

That's not to say that XENPAK wasn't a significant advance when it was first introduced (see Agilent, Agere Drive 10-Gig Ethernet ). It was one of the first modules to be pluggable into the side of a board, rather than from the top, allowing modules to be changed without taking cards out of the chassis. But technology moves quickly. Competing multisource agreements (MSAs) to XENPAK 10GBASE-SR were announced in March within a few days of each other. First was XFP, which is supported by a 44-vendor group including Broadcom Corp. (Nasdaq: BRCM), Brocade Communications Systems Inc. (Nasdaq: BRCD), Finisar Corp. (Nasdaq: FNSR), and JDS Uniphase Corp. (Nasdaq: JDSU; Toronto: JDU) (see 10 Vendors for 10 Gig). The XFP group announced the addition of 33 new members today (see XFP Touts Progress). The other contender is XPAK, which was introduced by Intel Corp. (Nasdaq: INTC), Infineon Technologies AG (NYSE/Frankfurt: IFX), and Picolight Inc. (see Trio Announce 10-Gig MSA). XPAK is a more direct "upgrade" for XENPAK because it sports the same XAUI (pronounced "zowie") electrical interface, and 70-pin connector.10G X2 Module is a type of 10 Gigabit Ethernet optical transceiver. X2 transceiver is based on Xenpak transceiver module, and it has same function with XENPAK transceiver. X2 Module also can use one transceiver to Compliant 10 Gb/s  fulfill all 10G Ethernet optical port function. X2 Transceiver is better for density installation for it is only half size of Xenpark transceivers.Its electrical interface for that host board can also be standardized and it is called XAUI (4 x 3.125 Gb/s).