First class

I told my students I would be writing this blog about the class – that will help me keep that resolution.

I think the first class went well. I offered three articles from today’s Globe, one on the impending restrictions on college loans for attending trade school, one on the future of the technology sector of the local economy, and an editorial on the cost in space and energy of sending photos as email attachments. The last one is just right for later in the semester (about 2/3 of the way through) but it’s the one the class found the most interesting, so it’s what we went with. The url is

The two interesting assertions are

The total amount of digital storage worldwide is approaching 1 zettabyte, or 1 million times the contents of the Earth’s largest library


Some analysts estimate that emailing a 4.7-megabyte attachment — the equivalent of four large digital photos — can use as much energy as it takes to boil about 17 kettles of water.

There’s no way we can deal with the second one now.

We did analyze the first. Turns out (reliable Google search) that the Library of Congress has about 118 million items (books, mss, etc).
A zettabyte is 10^21. So the question is

does 10^21 bytes for 1,000,000 times 118 million items

make sense?

Round the 118 to 100. Then the question is

does 10^21 bytes for 10^6 * 10^6 * 100 items

make sense.

That would be 10^7 bytes for one item, or 10 megabytes for one item.

In the text we estimated 1 megabyte for a book, so this seems to be about 10 times too large. But that 1 megabyte estimate is probably low, and they store other stuff too. So I believe the assertion in the editorial.

In class I was so rushed at the end that I fumbled the final computation, left out a factor of 1 million, and decided the editorial was wrong. I will have to do a mea culpa (and teach the lesson learned) when I meet the class again on Tuesday.

Maura Mast will teach Thursday’s class, on relative and absolute change. I did start on that material today. asking the class to compare a (hypothetical) library with 120 million items to the Library of Congress. The difference is 2 million items. Whether that’s a large number or not depends. In this case it depends on what you’re comparing it to, namely 118 million items. After a struggle (students trying to remember what they once knew, rather than thinking) we understood that it was less than 2 percent, so probably not a big difference, particularly given the fact that the 118 million is just an estimate to start with.

I may return to edit this comment later. In the meanwhile, I wonder if any students will respond.

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