
Five nines is a goal every marketing deparment would like to be able to claim. Normally, we'd be talking about computer system uptime, but I'm sure any marketing team would love to be able to talk about five nines of customer satisfaction, or widgits that pass muster; whatever. You'd like to be able to market your company by saying that your success rate is at least 99.999%.
Of course, that's not easy. In fact, it's really tough. In terms of computer system uptime, image your computer system has a 30 minute outage. You can imagine that happening easily enough - one server down, one mistyped command, one bug in the code. It happens, sometimes. However, if it does, that means that you need to have at least 3,000,000 minutes, or about 5 years, 8 and a half months of uptime up your sleeve to maintain your fine nines!
So, often five nines isn't considered to be worth the effort, regardless of how nice it would be from a marketing point of view.
[As a result, you can almost be sure that any company that does promises you five nines is not taking scheduled outages into the equation, and could very well only be promising you a predicted uptime, not a real uptime.]
However, regardless of the fact that five nines is really hard to achieve, I found it a little odd to see that BT are marketing themselves with the far less impressive one nine: at least 90% of payphones are working.
Maybe BT are hoping that most people won't be able to figure out that their claim means that, of the 75,000 public phones in the UK, up to 7,500 phones aren't working. That seems like an awful lot of phones to me.
I wonder how many of those phones that are broken are stand-alone phones, so that when it's broken, you can't just use the one in the booth next to it?