In Good to Great, Jim Collins proposes that one aspect that great companies get right is they have the right "denominator". In other words, they know which metric drives behaviour that aligns with their end strategic goal (rather than the nearest staging post on the way, or downstream effects like overall profitability).
Carrying forward my thoughts on energy use in telecom, perhaps we need a better measure to compare "dumb pipe" technologies. Telecom is one industry not upturned by the Death of Distance, because it itself is the industry tasked with masking out distance. The objective of a bit-haulage communications network is to cause the geographical migration of information. [Duh!] Disregarding Heisenberg and Einstein for a moment, all information is tied to a physical place at any instance in time. Every node in the network, be it optical or electrical, is there to direct the bits physically nearer to their destination.
So we want more miles. More bits. Fewer seconds to send those bits. And less energy to send them. Metres times bits as the numerator. Seconds times joules as the denominator. That makes bit-metres per Joule-second (bm/Js) our measure of the attractiveness of a communications technology. So unlike the usual method, we're not just looking at bits per second. A technology that can do 100Mb/sec but only projects those bits a metre is much worse than one that does 10Mb/sec to the other side of the world. Likewise if it takes a nuclear power station vs. an AAA battery to do it.
So let's take a few examples. Carrier pigeon with an aerodynamic flash drive strapped on its leg (we're not the first to try). First-class mail. FedExing hard drives around. A GSM phone. And a fiber-optic cable.
Carrier pigeon. 128Mb flash drive. That's 109 bits. Speed of pigeon 30mph. Weight of bird 500g. Metabolic rate 77Kcal/day = 77×4.2×103/3600/24 = 3.7kW (that's one hot bird!). Range 90 miles = 144,000m. 10,000 seconds. Result: (109x144×103)/(3.7×103x104x104) = 400bm/Js.
First-class mail plane. 2Kb of text on a letter. One letter 25g. One plane 50 tons of mail. Two million letters (we're packing them in!). 32 megabits of data. Boeing 757 fuel capacity 40,000 litres. Energy density of kerosene 46Mj/litre. Total energy 1.8TJ. Range 6000km. Cruising speed 900km/h. Flying time 24000s. Final result: (32×106x6×106)/(1.8×1012x24000) = 4×10-3 bm/Js.
Same plane. Filled with 200Gb hard drives, 1kg each inc. packaging. Assume we're limited by weight, not size. That's 50,000 drives, or 10,000,000Gb. About 1017 bits. Result of (1017x6×106)/(1.8×1012x24000) = 1.4×109 bm/Js.
Cell phone. Random Nokia model. Battery capacity 1300mAh. Duration 4h = 14,400s. Energy expended 1.3Ahx3Vx3600s = 14kJ. Data rate (reality, not spec. sheet): 20Kbps. Bits sent = 20,000 × 4h = 288mbit. Distance to tower: 10,000m. Result: 288×106x104/(14×103x4×3600) = 14,200 bm/Js.
Fiber optic: 5W laser. 1000gbit/sec. 9,000,000m from USA to Japan. Result? 1012x9×106/5 =~ 2×1018 bm/Js.
A quick summary:
| Method | Approx log10 bm/Jw |
| Snail mail | -3 |
| Carrier pigeon | 2 |
| Cell phone | 4 |
| Fedexed hard drives | 9 |
| Fiber optic | 18 |
Is this of any use to anyone? No idea, but it's one way to pass a Sunday afternoon. Distance projected always matters. Clearly for wireless the energy matters. For undersea cables, the energy matters (ever tried powering a repeater in the middle of the ocean?). For physical transport of bits, energy matters. Maybe for mains-powered land-based things it doesn't.
All a bit of fun! Enjoy finding the arithmetic and factual errors...
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