Editing Speed of light (section)

=== Small scales ===
In [[computer]]s, the speed of light imposes a limit on how quickly data can be sent between [[central processing unit|processors]]. If a processor operates at 1{{nbsp}}[[gigahertz]], a signal can travel only a maximum of about {{convert|30|cm|ft|0}} in a single clock cycle – in practice, this distance is even shorter since the [[printed circuit board]] refracts and slows down signals. Processors must therefore be placed close to each other, as well as [[Computer memory|memory]] chips, to minimize communication latencies, and care must be exercised when routing wires between them to ensure [[signal integrity]]. If clock frequencies continue to increase, the speed of light may eventually become a limiting factor for the internal design of single [[integrated circuit|chips]].<ref name="processorlimit">
{{Cite book
 |last=Parhami |first=B.
 |year=1999
 |title=Introduction to parallel processing: algorithms and architectures
 |url=https://books.google.com/books?id=ekBsZkIYfUgC
 |page=5
 |publisher=[[Plenum Press]]
 |isbn=978-0-306-45970-2
}}</ref><ref name="processorlimit2">
{{Cite conference
 |url=https://books.google.com/books?id=sona_r6dPyQC&q=%22speed+of+light%22+processor+limit&pg=PA26
 |title=Software Transactional Memories: An Approach for Multicore Programming
 |first1=D. |last1=Imbs
 |first2=Michel |last2=Raynal
 |year=2009
 |conference=10th International Conference, PaCT 2009, Novosibirsk, Russia, 31 August – 4 September 2009
 |editor=Malyshkin, V.
 |publisher=Springer
 |isbn=978-3-642-03274-5
 |page=26
}}</ref>