The Physics of the Internet
Computer Science 01i
Introduction to the Internet
• Atoms vs. Bits
• Measuring Information
About this Lecture
• This is the most abstract theoretical
lecture of the quarter. It gets easier. :)
• The purpose is to give you enough theory
to deepen your appreciation of the
Internet and its power.
• Don’t sweat the details! This is just to give
you a feel for what we’ll talk about later.
Atoms vs. Bits
• We are used to thinking of them as the
same, but they’re very different!
The “smallest recognizable” piece of matter
Smallest piece of information (“1s and 0s”)
Think about a book
• It has physical form: atoms
• It has information: bits
• How are these two things different?
Bits are cheap
• Computers make manipulating bits cheap
• Electronic networks make communicating
postal system vs. phone system
phone system vs. a computer network
• email, faxes, are they different?
Our ability to manipulate each is
growing at vastly different rates
• Power over bits: exponential growth!
• Power over atoms: linear at best
• One version:
“The power of the microprocessor doubles
approximately every eighteen months.”
Gordon Moore, founder, Intel Corporation
• Moore’s law may someday hit a wall,
but for now, bank on it.
• Nothing similar for atoms
Aside: `Net is growing fast
• The “size” of the internet doubles about
every 20 months (number of users)
• No telling how much information is added
• Electronic commerce
up 230% from 1998 to 1999
about the same for 1999 to 2000
2000 to 2001? “only” 150%?
Growth Downsides: 1999
• Sites get overloaded
• Commerce sites made big mistakes last
• “If hard data were the filtering criterion
you could fit the entire Internet on a
Cecil Adams, “The Straight Dope Tells All”
Digital vs Analog
• People often use “bits” and “digital”
interchangeably, but there is a subtle
• Bits can come in digital or analog versions
• The digital version is less accurate (!),
but much more easily manipulated
Atoms vs Bits: Conclusion
• The growth in our ability to manipulate
bits in the next few decades will affect
society as much as the growth in our
ability to manipulate atoms did in the
years of the industrial revolution.
• This class is about a major part of that
People of the ‘Net:
• Bits vs Atoms is his idea
• Founder of the MIT Media Lab
• More of his ideas can be found in his
book, Being Digital.
• “In the past shoes could stink,
In the present, shoes can blink,
In the future, shoes will think.”
• A single bit is an awfully small piece of
Byte Eight bits
Kilobyte About one-thousand bytes. One “K”.
Megabyte About one-million bytes. One “Meg”.
Gigabyte About one-billion bytes. One “Gig”.
Terabyte About one-trillion bytes.
• Don’t worry too much about these words
A better way to think about it
• A single spaced page of text:
about 2 kilobytes
• A 3” by 5” full color picture:
about 10 kilobytes
• A four minute song on a CD:
about 35 megabytes
• A full length movie
about 6 gigabytes
The information in CDs and
movies is different from
the information in text and
• Measures information per a unit of time
• Plumbing analogy:
bandwidth measures pipe capacity or
Also measures processing power
• Bytes or kilobytes or megabytes
• Typical phone connection to the Internet
today is 56 kilobits per second
(actual is about 35-45 kilobits per second)
• Ethernet (offices and campus housing) is
10 megabits per second
(actual is about 7-8 megabits per second)
• Higher speed connections are available
What does that mean?
• Remember the size of a page of text?
About 2 kilobytes
phone lines take about 1/2 seconds
Ethernet appears instantaneous
• A small picture is about 10 kilobytes
phone lines take about 2 seconds
Ethernet still appears instantaneous
What about sound and movies?
• CD quality audio:
megabytes per second
Four minute song
• phone line requires almost 2 hours
• Ethernet requires about 35 seconds
• Television quality video:
hundreds of megabytes per second
A full length movie? Not yet =)
• Internet speed and capacity are about
• Well, not completely...
What else is there?
• A semi-trailer loaded with DVD discs
driving from Palo Alto to San Francisco
has a greater bandwidth that the fastest
portion of the internet
Terabytes per second!!
• So what is missing?
• The overhead required to send any
information whatsoever (like shipping)
• The amount of time it takes to send no
information at all!
• The latency of the semi-truck is about
More on Latency
• Latency is a big problem for modems
• Certain parts of the internet magnify this
• Fixing latency problems is much trickier
than fixing bandwidth problems
• Is a 747 three times as fast as a 737?
• A 747’s bandwidth is much greater than
• But their latency is about the same
• What plane could you use to decrease
Fun facts about human bandwidth
• Brain: over 10 gigabits per second
• Eyes: 10 megabits per second
• Skin: 1 megabit per second
• Ears and nose: 100 kilobits per second (each)
• Taste: 1 kilobit per second
• Consciousness: less that 40 bits per second
-- The User Illusion, Tor Norretranders
Sources and further reading:
• On bits vs Atoms:
“Bits and Atoms”
David Micko, Fingerhut Corporation Webmaster
• On Bandwidth and Latency
Computers@Home electronic magazine
“It’s the latency stupid!”
Stuart Cheshire, Stanford Graduate Student