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."

L1 cache reference..............................0.5ns

Branch mispredict.................................5ns

L2 cache reference................................7ns

Mutex lock/unlock................................25ns

Memory reference................................100ns

Compress 1K bytes with Zippy..................3,000ns

Send 2k bytes over 1Gbps network.............20,000ns

Read 1MB sequentially from memory...........250,000ns

Round trip within datacenter................500,000ns

Disk seek................................10,000,000ns

Read 1MB sequentially from disk..........20,000,000ns

Send packet CA->Netherlands->CA.........150,000,000ns

http://www.regexprn.com/2009/12/numbers-everyone-should-know...