Re: Laptop safe for flight in planes?
On Wednesday 23 February 2005 09:44, Tim Connors
<tconnors+debianlaptop@astro.swin.edu.au> wrote:
> Um? Actually...., you know your 1.4GHz machine? It emits 1.4GHz, as well
> as every harmonic above - 2.8, 4.2, 5.6,.... Ghz. And if you are only
> executing an instruction every n clock cycles, then you also emit at
> 1.4/n, 1.4*2/n, 1.4*3/n,.... Ghz.
Have you used a spectrum analyser to prove this?
I doubt that you could demonstrate a laptop emitting a frequency of clock/3
because of executing an instruction every third cycle. It may emit such a
frequency anyway because of it being the FSB speed, the on-chip cache speed,
or something else. It may emit such a frequency due to speedstep type
technology allowing the clock to run at a lower speed. But I doubt that you
could turn such a frequency on/off by changing the code that is being run.
I believe that CPUs tend not to be properly idle, they are always ticking over
even if the CPU has executed HALT and is waiting for an interrupt unless you
use speedstep or similar technologies.
However I agree with your main point, that the system can emit many
frequencies. The PCI bus has it's own frequency, the DRAM has it's own
frequency, and whatever is done to convert 16V DC to 110V (*) for the
back-light of the screen also probably causes some emissions too.
I believe that the people who travel by plane have a higher incidence of
mobile phone use than average. On a flight with 300 people I think it's
reasonable to expect that there are at least 100 mobile phones. I think it's
reasonable to expect that at least 1% of people forget to turn their phone
off before the plane takes off. Therefore I believe that the average number
of operational mobile phones on a 747 at take-off is at least one, some
flights may have many phones operational at take-off. The fact that there
has never been a plane problem tracked back to mobile phone use suggests to
me that planes are built to stand such things. Besides, if a plane could be
brought down with a phone or a wireless device then terrorists wouldn't
bother using bombs...
(*) The last time I took a laptop apart while it was turned on I got a nasty
shock and later measured the voltage at 110V. I am guessing that newer
laptops still use the same voltage but haven't been keep to repeat the
experience...
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