W dniu 2013-01-18 18:14, retired mainframer pisze:
:>: -----Original Message-----
:>: From: IBM Mainframe Discussion List [mailto:[email protected]] On
:>: Behalf Of R.S.
:>: Sent: Thursday, January 17, 2013 10:32 PM
:>: To: [email protected]
:>: Subject: Re: silicon photonics - faster than copper
:>:
:>: W dniu 2013-01-17 18:23, retired mainframer pisze:
:>: > While photonic components (switches, etc) may be faster than the
:>: current
:>: > semi-conductor ones, can the wiring really be a factor. Don't both
:>: > electricity and light move at c?
:>:
:>: Neither light nor electricity move at c.
:>:
:>: Speed of light depends on the media. c is for vacuum. For fiber optic it
:>: is c/RI RI - refractive index, approx. 1.46
:>: So for the calculations people tend to use speed of light (still in the
:>: FO) as 200 000 000 m/s.
:>:
:>: Now, speed of electricity is higher it's approx. 3/4 c. However I can't
:>: remember explanation for the number.
This implies that the faster speed of the optical system has almost nothing
to do with the wiring as claimed.
Thus we have another example of brain-dead journalism. Either the reporter
didn't understand what he was told and chose to embellish it incorrectly or
he simply repeated whatever buzz words he got from the PR department.
Neither case engenders confidence.
Well, you demand the reporters to have knowledge. Bad. :-)
I use to teach about SAN, FICONs and fiber optic technology in general,
usually the students are IT professionals, but believe me I have to
explain them the difference between throughput and speed, people don't
feel it's "two-dimensional".
My explanation (loosely translated to English): when you double the
"speed" expressed in Gbps, for example from 8 to 16 GBps that means your
train now have doubled number of cars (carriages). But the speed of
light remain unchanged so it will take same time to travel from Lodz to
Warsaw. Be aware, that very often you send small packets, only
locomotive is sent. So, speed (Gbps) cannot compensate the distance.
Speed helps with bulk data transfer, but doesn't help with "interactive
conversation".
BTW: Why people use Fiber Optics?
In very short:
distance (not the case)
EM interference (lack of them) - that's the reason!
Big speed (in Gbps) available - copper is limited by the above, FO is not.
BTW2 Google for AVAGO MicroPOD and US Conec PRIZM LighTurn - the future
is now. ;-)
--
Radoslaw Skorupka
Lodz, Poland
--
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