<story><title>The computers are fast, but you don&apos;t know it</title><url>http://shvbsle.in/computers-are-fast-but-you-dont-know-it-p1/</url></story><parent_chain><item><author>forinti</author><text>On a 3GHz CPU, one clock cycle is enough time for light to travel only 10cm.&lt;p&gt;If you hold up a sign with, say, a multiplication, a CPU will produce the result before light reaches a person a few metres away.</text></item></parent_chain><comment><author>dragontamer</author><text>&amp;gt; If you hold up a sign with, say, a multiplication, a CPU will produce the result before light reaches a person a few metres away.&lt;p&gt;The latency on multiplication (register input to register output) is 5-clock ticks, and many computers are 4GHz or 5GHz these days.&lt;p&gt;5-clock cycles at 5GHz is 1ns, which is 30-centimeters of light travel.&lt;p&gt;If we include L1 cache read and L1 cache write, IIRC its 4 clock cycles for read + 4 more for the write. So 13 clock ticks, which is almost 70 centimeters.&lt;p&gt;------------&lt;p&gt;DDR4 read and L1 cache write will add 50 nanoseconds (~250 cycles) of delay, and we&amp;#x27;re up to 13 meters.&lt;p&gt;And now you know why cache exists, otherwise computers will be waiting on DDR4 RAM all day, rather than doing work.</text></comment>
<story><title>The computers are fast, but you don&apos;t know it</title><url>http://shvbsle.in/computers-are-fast-but-you-dont-know-it-p1/</url></story><parent_chain><item><author>forinti</author><text>On a 3GHz CPU, one clock cycle is enough time for light to travel only 10cm.&lt;p&gt;If you hold up a sign with, say, a multiplication, a CPU will produce the result before light reaches a person a few metres away.</text></item></parent_chain><comment><author>generalizations</author><text>I ran across an animation once that showed graphically the time it takes light to travel between the planets and the sun. It&amp;#x27;s weird, but light doesn&amp;#x27;t seem that fast anymore.</text></comment>