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Mailing Disks is Faster than Uploading Data
CowboyRobot writes "Who would ever, in this time of the greatest interconnectivity in human history, go back to shipping bytes around via snail mail as a preferred means of data transfer? Jim Gray would do it, that's who. And we're not just talking about Zip disks, no sir. We're talking about shipping entire hard drives, or even complete computer systems, packed full of disks.
David Patterson (one of the developers of both RISC and RAID) interviews ACM Turing Award winner Jim Gray." Back in school we always had a saying, "Never underestimate the bandwidth of a station wagon filled with backup tapes." Seems like that still holds true.
This reminds me of how data is collected for SETI@Home:
After the data is recorded onto tapes at Arecibo, they are shipped back to the SETI@home lab in Berkeley, California. The data are then broken up into workunits, which are sent out to the client screensaver program for candidate signal detection. So far, SETI@home has generated 189,598,882 workunits from the data received from Arecibo. SETI@home has split 1,139 tapes, meaning that the average tape yields 166,709 workunits. This is somewhat lower than the optimal yield of roughly 200,000 workunits per tape because of radio frequency interference, gaps in recording, problems with the recording equipment, etc.
I think a work unit is 65,536 bytes. Even if it takes a week to ship one tape, you can't beat that throughput! But the latency is the worst.
A programmer is a machine for converting coffee into code.
What a great example you picked! Cable TV companies are pumping dozens of digital movies accross their system at once, live. Yet they crimp your upload speed to DSL rates or lower,
very wrong.
But enough truth to fool people into believing what you said.
You are correct in saying that a digital cable system pumps out lots of bandwidth. They do. A movie chan is generally about 4mb/s, possible 8. A chan such as the shopping chan may be 1mb/s. So your cable company with 100 chans is pumping out approx 400mb/s.
Thats a lot of data.
But it is broadcast. Each customer is not individually downloading 400mb/s each. They are sharing *one* broadcast. It is not one stream per customer, but one stream is shared between all customers.
To use a cable for internet, assuming no TV is being broadcast, you can share that 400mb/s between all your users. Customers will have 4kb/s (thats kilobits) EACH (assuming its all shared equally). Not huge.
Obviously this is not the whole story. Your bandwith is shared between all customers on a node of the cable network (think of them as hubs). If you are the only person in your node, you will get full bandwidth. A node could cover tens, if not hundreds of thousands of users. If every person on your node is using the net to download porn, you will have a very slow connection (better using a modem). Also, the cable company wants to not just do internet, but TV too! In fact, most of the bandwith is used with TV/Movies.
So, they end up using part of their bandwith for internet, and part for broadcasting TVs.
How much they set aside for each is a buisness decision, as well as a technology one. If they sell cable internet, the costs are huge, setup, support, network, etc. Costs go up *per user*. Costs for TV is small (ish). Pay for content (movies), get money in from advertising, users, etc etc. No big support costs, no extra costs for bandwith etc etc. One stream can support hundreds of thousands of users.
It is both a technological problem *and* a buisness problem. They aren't giving you small limits cause they are afraid you will download videos. Don't be paranoid. They don't give you unlimited bandwith cause they can't, and it costs them a lot anyway.