For those that did not find Scott Elder's comment, here it is: Wall at 4 GHz? Scott Elder 9/13/2014 3:59:43 PM NO RATINGS LOGIN TO RATE This comment doesn't make sense: "Silicon digital logic hits the wall at 4 GHz, but we can produce small gallium arsenide [GaAs] analog circuits switching at 100 GHz today and 400 GHz in the not too distant future," The only part of silicon that hits a "wall at 4GHz" is power. Huge 500nm silicon devices have had ft,fmax of 5GHz or more for 20 years. Today, silicon is at sub-20nm. Planar silicon MOSFETs are knocking on the door of 1THZ with a T for Tera. The silicon world (read: Intel) just stopped focusing on ft because of power limits and now focus on density with multi-core computing using finfets (lower ft than planar). For non-scientific applications, technology is not about logic circuit speed much anymore. Furthermore to compare the speed of an analog circuit to a digital circuit is misleading. Analog is always faster for the same technology because the circuit can perform useful functions (i.e. gain) closer to the device ft regardless of the technology. If one wants to compare two technologies the conversation needs to factor in power, area, speed, and cost of like circuits. The study between Si and GaAs has been on going for at least 50 years now and silicon is still on top. And it is on top because the technology world makes decisions based upon all four parameters collectively whereas NASA, DOD, ESA, CERN, and other low volume, scientific-centric enterprises don't care much about cost. The 1980's mantra that "GaAs is the silicon of the future. It is and always will be." seems to still apply. Engineers just can't get their minds past the potentially available 3x improvement factor in speed; cost be damned. In many respects the arguments in this article are similar to the arguments made during the FPGA wars. Actel and Quicklogic with their lower power technology could never get ahead of the SRAM based approaches of Xilinx and Altera. This was because the purported inferior SRAM approaches were always at least one technology node ahead. A similar claim made in this article. When I see GaAs competing on a cost-speed-power-size basis, I will rethink my position. "Those who fail to study history are doomed to repeat it."