Anounced September 2015
Rewrite and update April 2018: This is a Tomahawk with 128 SerDes
running at 20 Gb/s. 64 ports not withstanding, this is not a Tomahawk2.
The 7260QX-64 is
covered in a combined data sheet.
A surprise is that this the only QSFP switch that cannot
use a splitter to farm ports out to 4 x 10 Gb/s. It appears the SerDes
are locked at 20 Gb/s so that a pair of lanes has the right speed to make
a 40 Gb/s port along with an undisclosed gearbox.
An article September 14, 2015 in nextplatform.com Timothy Morgan said:
There is a variant of this box called the 7260QX-64 that uses the Tomahawk ASIC but only supports 40 Gb/sec speeds (using QSFP+ ports), only 5.12 Gb/sec of switching bandwidth, and only 16 GB of buffer capacity. The aim of this machine is to be a lower cost spine switch for 40 Gb/sec networks that also burns less power than the older 40 Gb/sec switches based on 10 Gb/sec lanes and the Trident-II chips. This switch will cost around $1,000 per 40 Gb/sec port, says Hull, at list price. Port-to-port latency is at 550 nanoseconds. The 7260QX-64 will be available in the fourth quarter.
He said 16 GB but he meant 16 MB. The variant to
which Tim is referring references the 7260CX-64 which Tim says
contains 4 Tomahawks. I think he has not accounted for the ASIC interconnect
Here's an Arista family family overview for Tomahawk.