August 05, 2002

Five Nines Instead of Nine Fives

"Five nines" means that if you express the reliability of a system numerically, the first five digits are nines: there is a greater than 99.999% chance that the system will do what you hope it will in any particular operation, and only one chance in 10,000 that something will go wrong and break. "Five nines" is a joke--as in, "You wanted nine fives of reliability? I thought you said nine fives!" i.e., that the system will perform as hoped for 55.5555555% of the time--barely more than half the time. The rest of the time something will go badly wrong.

Back when I used Windows machines and pre-OS X Macintoshes, it felt like my computer systems had nine fives of reliability. You learn strange habits when you know that the blue screen of death--or the bomb icon--will appear at least twice a day. You save after every paragraph. You don't leave one program open, with a task half completed, while you switch context to another: you know there is a good chance that you will never return to the old program. You write a lot of things down on scraps of paper to try to keep track of what is going on.

But now--with Macintosh OS X--I have a computer with five nines of reliability. I can leave--I do leave--fourteen programs open at once. Seven of them have half-completed tasks, or notes I want to remember, or are simply left open to jog my memory that I need to work on something. I used to fear performing any "background" tasks while working: What if the foreground application takes the computer down? What then? Thus long background tasks would only get done while the computer was doing nothing else--and while I was hovering over it, worrying that even so something would go wrong.

What's the gain in efficiency from having five nines instead of nine fives of reliability? It feels like 20% or so.

However, one thing still goes wrong: Microsoft Internet Explorer crashes regularly. It doesn't take down the computer--it just takes down the application and its associated windows. It is an unpleasant reminder of what computing used to be like...

Posted by DeLong at August 5, 2002 07:08 PM | TrackBack


I have eleven Mozilla windows open right now in OS X on a mere G3 iBook, along with a mail program, Word, Excel, iTunes playing a CD, BBEdit, two terminal windows, Stickies, and an AIM client. Better, Mozilla keeps all the windows tidily arranged in a convenient tabbed layout. And I can save a pointer that will reopen all eleven URLs exactly where I left them.

I've seen Mozilla for OS X crash -- on the order of once or twice a month. Much better than MSIE.

Posted by: Patrick Nielsen Hayden on August 5, 2002 09:08 PM

Although not quite five nines yet, Mozilla for Mac OS X ( might be the solution to the frequent IE crashes. Using much the same open source under pinnings as darwin (the foundation of OS X) mozilla has remarkable stability and the same hacker driven pursuit of perfection.

Posted by: Stephen A. Kupiec on August 6, 2002 01:31 AM

Thanks for the post, Brad, and for the comments, Patrick/Stephen. When I buy a computer next, I'll get a Mac.

I'm particularly excited by the idea that OS X is Unix based. How many applications have people seen available for OS X, which weren't available on a Mac before?

Posted by: Barry on August 6, 2002 04:23 AM

There are a *ton* of apps for OS X. If there is a Unix version of an app, there is probably a OS X version - not to mention all the cool tools built into OS X like perl, php, AppleScript, vi, pico, emacs. I also have python and mysql running on my Powerbook. It is indeed the best of both worlds.

Check out for all the open source software you can handle.

Posted by: Larry Staton Jr. on August 6, 2002 05:28 AM

Thanks, Larry.

Posted by: Barry on August 6, 2002 07:22 AM

Yes, OS X rocks, but in fairness to MS, I've found Windows 2000 Professional (alias NT 5) very stable.

Opera also has an OS X browser, but I don't know the robustness.

Posted by: Andrew Lazarus on August 6, 2002 08:20 AM


Why is NT5 so much more stable than previous NTs? It was never clear to me from the little I knew about NT's design where the instabilities had come from in the first place...

Posted by: Brad DeLong on August 6, 2002 01:53 PM

'Why is NT5 so much more stable than previous NTs? It was never clear to me from the little I knew about NT's design where the instabilities had come from in the first place...'

Application crashes are outside the scope of the operating system; it can just control them. NT4 was pretty good at that, and 2k is pretty much perfect; I have yet to see an application crash take down a 2k system.

As to the operating system itself crashing, the causes are:

1) Bugs in the operating system.

2) Bad hardware drivers (video card, sound, whatever) taking the entire system down with them when they fail.

2k, near as I can tell after 2(3?) years of use, has very little of 1); I have yet to have a crash that's an OS bug.

Unfortunately, there's still a lot of bad drivers out there, so it's a crapshoot if you buy anything but top-of-the-line (Nvidia, creative labs, a name-brand motherboard) hardware. That said, I average a crash of any sort every, oh, 3 months of 4+ hours/day use.

Wierdly, XP is less stable than 2K. No idea how they managed that.

Posted by: Jason McCullough on August 6, 2002 04:22 PM

Oh, I forgot: the reason the new Macs are so stable compared to the old ones is that they threw out the old operating system. They're now using some sort of BSD unix variant with a GUI on top.

Posted by: Jason McCullough on August 6, 2002 04:24 PM

Speaking of stability... Netcraft runs a real-time list of sites with the longest uptimes. The whole list is a bunch of BSD sites with an occasional Linux, or Solaris, or IRIX...

Posted by: Nikolai Chuvakhin on August 6, 2002 11:56 PM

I've got win xp, i've had it for three months, and i've never had a system crash, just program crashes. I guess all operating systems are stable now.

Posted by: on August 8, 2002 06:16 PM
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