Sysadmin Field Notes - April 2008 Archives

April 29, 2008

Fortune thinks ATT wants to pick up $200 of your iPhone.

This could mean big, big things for Apple if it's true. I think this strategy makes the 10 million phones by the end of the year goal look like a drop in the bucket. Apple's not in the habit of selling anything at a loss though, but that's okay here since it's ATT that would pick up the tab.

The question is, why would they? And why wouldn't they at launch? Was it so calculated that ATT knew demand would drive 5-6 million phone sales that they could rake in bucks for, in return for taking the risk on the iPhone, and then after a year and version 2.0 they'd announce the subsidy, to go deeper into the market?

Brilliant strategy if true. For one it's obvious; it's just pricing things like the market will bear. Second, this makes the iPhone like an iPod; it puts it into kids' price ranges. Can you say "ubiquitous"? I knew you could.

So at the expense of some cash, ATT gets to own the market for what could be an iPhone-like domination of the phone market for the next 5-10 years. Bold.

April 18, 2008

Someone got a hold an old archive of all things Infocom. The post talks about a sequel to Hitchhiker's Guide to the Galaxy, but what I find really interesting is the e-mail tone. They read like letters, back and forth across a great divide. Today's version I suspect would look very different.

April 9, 2008

I don't know why this just popped into my head, I've thought about before but apparently never mentioned it. The Nyquist limit is most accurately described on wikipedia, but here's a simple way to visualize it that I've always used to explain it.

Imagine a video camera, shooting 30 frames per second. You walk into the frame, and your actions are very accurately recorded. Now slow down the camera to 1 frame every 60 seconds. The camera takes a picture, then you run through the frame in 2 seconds. 60 seconds later, it takes a picture and it's like you were never there, even though you were. You were faster than the sampling rate of the camera, so it didn't capture you at all. It -can't- if you continue to move that fast. You have to slow down, or speed up the camera. That's why the hard limit.

Now, you if you vary your speed, you can play with the frequency of how often you show up. So let's say the camera it still running at 1 frame a minute, and your pacing back and forth, spending 5 seconds in the frame out of every 45 seconds. So your real rate of passing the camera is once every 45 seconds. So the camera starts, as do you, and your first pass comes at 45 seconds and you're gone. The camera fires, and there's no you. You pass by again at 1m:30s...then 2m:15s...then at 3m. The camera is firing then because it fires at 0s, 1m, 2m, etc...So you're caught on film. You're next pass is 3m:45s, then 4m:30s, then 5m:15s, and 6m, and you're caught on film again at the 6 minute mark.

So you're real rate of passing by is every 45 seconds. But according to the film, you're only passing by every 3 minutes. That's aliasing. Because the sampling rate isn't fast enough to capture your frequency, you are "aliasing" to a different frequency. From 45s to 3m. You can imagine when capturing music with samples that this would do baaaad things to the soundwaves, which is why digital audio systems filter out high-frequency sounds somewhere around the Nyquist limit, so they don't alias to the wrong frequencies and destroy everything.

This explanation isn't perfect of course, but I have found it useful to explain the concept.