Friday, September 10, 2004

Of Time (and Terabytes)

'Life caching', it's called. Attach a wireless webcam and microphone to your bonce and let a continual stream of all your comings and going get squirreled away for viewing some other lifetime.

Actually, the idea has its uses:
  • '...unhand me, you randy brute! You're on candid camera!'
  • '...if you want a witness, my website saw it all!'

There is a catch of course: all this information has to be stored somewhere. Part of the recent interest in the idea is that mass storage is getting pretty... well, capacious! It wasn't that long ago that terabyte storage was the province of major computing installations. Now it can be obtained off the shelf for only a few hundred dollars.

Is it enough?

Well, I started doing a bit of calculating:
Suppose we wanted to store all sight and sound experiences for a lifetime. If we take our alloted span to be a generous 100 years , that's about 3e9 seconds. Smooth streaming video requires about 30 frames/sec, so that works out to be around 1e11 frames.

Now then, how much data in a frame? We want full surround vision (ie 4*pi steradians, please!) in 24 bit colour.
The average pixel on a 40 cm (1280x1120) screen is about 400/1280 ~ 0.3 mm across.
Given we have comfortable viewing at about 50 cm, that requires about 4*pi*(500)^2/(0.3)^2 ~ 35 million pixels, or 1e8 bytes to paste our entire viewing sphere to the same resolution in 24 bit colour.

So, that works out to be 1e19 bytes, or 10 million terabytes. I'm not going to include sound, as it needs a good deal less storage than vision, and could easily be packed away in some corner of the figure quoted here.

OK, so I've been rather generous with my requirements, and I've given no thought to data compression. The basic point is that full on life caching is a ways off yet.

Still, you could get started now, and ramp up your storage as it becomes cheaper.


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