For those interested or surprised by the quote "There is a huge performance difference between memory and disk. RAM is typically 100x to 1000x faster than disk" you may also enjoy Jeff Dean's (of Google) "Numbers Everyone Should Know."<p>L1 cache reference..............................0.5ns<p>Branch mispredict.................................5ns<p>L2 cache reference................................7ns<p>Mutex lock/unlock................................25ns<p>Memory reference................................100ns<p>Compress 1K bytes with Zippy..................3,000ns<p>Send 2k bytes over 1Gbps network.............20,000ns<p>Read 1MB sequentially from memory...........250,000ns<p>Round trip within datacenter................500,000ns<p>Disk seek................................10,000,000ns<p>Read 1MB sequentially from disk..........20,000,000ns<p>Send packet CA->Netherlands->CA.........150,000,000ns<p><a href="http://www.regexprn.com/2009/12/numbers-everyone-should-know.html" rel="nofollow">http://www.regexprn.com/2009/12/numbers-everyone-should-know...</a>