What does four 9's mean?

[Meg I]

In the interview with the CEO and CIO, the last question asks about the service level agreement in place with transmaster? The CIO responds by saying "They have committed to have their site available four 9's." I have not heard this phrase before. Can anyone shed any light?

[Vincent O'Sullivan]

Don't you just hate dumb jargon!

[Edy Yu]

Yes, it is 99.99%.
But usually, people use five 9's when they talk about the availability.
Any way, I interperet the CIO's words to "they have made their site 99.99% of time available"

[Meg I]

Thanks guys!
This phrase must be an americanism as I have never heard it before. I have asked several of my associates who've worked in IT for years and they haven't heard it before either.

[Ron Newman]

It must be a regional Americanism because I've never heard it here in Boston.

[Tim Duncan]

Specialist jargon rather than regional. We've heard of it over this side of the pond (i.e. in the UK).

[Edy Yu]

I heard it thousands of times in mid-west.
Heard it once in Baltimore.

[Rufus BugleWeed]

They are promising to be down only 52 minutes a year. Is it a minute here and a minute there? Or does it come at the peak of the Thanksgiving booking rush?