The Difference Between 5 and 6 Nines

We will occasionally pepper in a few brainteasers at the end of our interviews.  Yes, they are sometimes the you-don’t-bury-survivors type questions.  And then there’s the cube question which I have written about previously.  One of the guys on my team likes to ask “port association” questions.  He gives a port number and the candidate provides an answer.  It is kind of fun to hear “80.”  “HTTP.” “443.”  “HTTPS.” “21.” “FTP.” “789″ “Pardon me?” The other evening a co-worker was sharing a past interview experiences.  He was interviewing for a technical business analysis role and they asked him, “Is the clock on your VCR blinking?”  To this, he replied, “What is a VCR?”  Not a bad question and not a bad answer in my book.

Joel Spolsky translated uptime percentages to allowable time/year outages in today’s Five Whys article.  For example, an SLA stating something like 99.99% uptime allows for 52.59 minutes of downtime per year.  Where am I going with this?  How’s about this for an interview question: “What is the difference between 5 and 6 nines?”  This question will probably generate some interesting answers.  There will be a good number of individuals who are familiar with the term and they will be able to speak to the question.  Some might provide the difference between 99,999 and 999,999.  Others will perform the translation in their heads, give the correct answer down to the second and knock my socks off.  If you find yourself sitting in on an interview with me, look out.  This question is coming — or not.