Slashdot Mirror
Sun Turns to Lasers to Speed Up Computer Chips
alphadogg writes to mention that Sun is attempting to move from the typical design of multiple small chips back to a unified single-wafer design. "The company is announcing today a $44 million contract from the Pentagon to explore replacing the wires between computer chips with laser beams. The technology, part of a field of computer science known as silicon photonics, would eradicate the most daunting bottleneck facing today's supercomputer designers: moving information rapidly to solve problems that require hundreds or thousands of processors."
On chip they are pumping the signal over a traces with mm range lengths and um range widths, off chip it's over traces with dm range lengths and mm range widths. Timing and power consumption are hard enough problems on chip, off chip they become much harder ... not to mention that most of the power consumed either goes into EM or gets coupled into other signals.
Serial connections help with the timing, but do diddly for power and noise. That's where optical comes in.
In fact electrons in your typical electrical wire don't move anywhere near the speed of light.
http://www.eskimo.com/~billb/miscon/speed.html
I don't know if this is a serious question or not, but one assumes that the lasers will operate in completely sealed environments (e.g. inside an IC package) or over optical fibers if they need to traverse free space. I think the intra-package situation is probably more common; you could communicate from one core to another on the same die using a laser rather than a wired interconnect and hopefully have less interference/RF/capacitance issues to deal with. This also makes sense given what I know about modern types of laser diodes (especially Vertical Cavity ones) -- they can be created on silicon wafers through similar processes to the way transistors are laid down.
I can't think of any good reason why you'd just be aiming a laser through the empty space inside a PC's case.
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If I understood correctly this is not about single wafer design but exactly the opposite: regaining the speed of 'single wafer design' with multiple chips by using optical communications between chips increasing the inter-chips bandwidth (normally intra-chip bandwith is much higher than inter-chip bandwith so this is a bottleneck).
Why, why, why do people submit second-hand links to Slashdot?
The byline of the Seattle Times story is "John Markoff New York Times". 5 seconds with Google's site:nytimes.com reveals the original story with better explanation and more quotes from Sun personnel.
=S
When you look at a wire, or printed trace on a PCB it is not the resistance that limits how fast you can send a signal. It is inductance and capasitance that act like a low pass filter. We don't care how fact eletrons travel in wire what we care about is how fact we can change the voltage in the wire. We send data by changing voltages not by sending electrons.
It was quite the smoking crater last time around. Maybe technology has improved since then...