Re: speed of light hitting a mirror

Tom Roberts wrote:
John Kennaugh wrote:
Where a nanosecond is the rather long period of time your out of date, slow, 1GHz Pentium processor used to take to complete a clock cycle before you replaced it with a faster, less pedantic processor :o).

Aparently you have fallen victim to Intel's marketing hype.

Not me, but it is something that most people can relate to. To me nanoseconds are everyday units. It is what you use to measure such things as propagation times in logic circuits and propagation times in transmission line interconnections. Most speed increase in computers has been achieved by more RAM and its clever usage but I was designing high speed logic circuits (140MHz) 30years ago and one look at the PC mother board tells me that the data access rate even to the RAM cannot be very high. My guess is 10 to 20MHz max. Not that it matters because the Achilles heal is the hard disk which is why my computer has just taken 80,000,000,000ns to boot up.


For ~90% of PC users, the CPU clock speed is almost irrelevant.

Quite so. At the end of the day we are still accessing data by mechanical means from magnetic storage. We have got amazingly good at it but it is still no different in principle to magnetic tape which really is ancient technology in terms of electronics.

What really matters is the memory speed (not FSB speed unless it slows down the memory).


BTW if you consider a 1GHz Pentium "out of date", your memory must be quite short. Many of us remember 1MHz CPU speeds, and some are still in use....

I watched that excellent film "Apollo 13" and realised that yes, they really were using slide rules then. We have come a very long way in a short time. It wasn't that long ago that I upgraded my computer by fitting a 'massive' 20Meg hard disk.

I think that we have shot ourselves in the foot. If programmers had to use memory as efficiently as they did then the hard disk would have been replaced by a solid state device and the speed of computers would really have increased but the squandering of memory by programmers means that the hard disk is still the only thing which can cope with it all. When I install a program these days I do wonder how much of it is really necessary.


      Off topic, but I couldn't resist.


My point was still a valid one that with today's technology light can no longer be considered unimaginably fast.
It is a mere 1 ft/ns in every day units.



Tom Roberts tjroberts@xxxxxxxxxx 

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John Kennaugh
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