Sidebar: Commonly used prefixes

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Memory and storage capacity are measured in bits – the number of ones and zeros that can be stored. Data transmission rates are measured in bits per a unit of time, typically bits per second. Since capacities and speeds are very high, we typically use shorthand prefixes. So, instead of saying a disk drive has a capacity of 100 billion bits, we say it has a capacity of 100 gigabits.

The following table shows some other prefixes:

Note that the numbers in the fourth column are approximate. For example, strictly speaking, a megabit is not one million (1,000,000) bits it is 1,024 x 1,024 (1,048,576) bits. Still, they are close enough for most purposes, so we often speak of, say, a gigabit as one billion bits.

Capacities and rates may also be stated in bytes rather than bits. There are 8 bits in a byte, so dividing by 8 will convert bits to bytes and multiplying by 8 will convert bytes to bits.

The NSFnet was the first nationwide Internet backbone, but today there are hundreds of national and international backbone networks. High speed links now commonly transmit 10 gigabits per second, and a single fiber can carry multiple data streams, each using a different light frequency (color). 1 Of course, progress continues. For example, Siemens researchers have reliably transmitted data at 107 gigabits per second over a one hundred mile link and much faster speeds are achieved in the lab. 2

There has been similar improvement in local area network (LAN) technology. Ethernet is the most common LAN technology. When introduced in 1980 Ethernet links required short, thick cables and ran at only 10 megabits per second. Today, we use flexible wires, Ethernet speed is 10 gigabits per second today, and standards groups are working on 40 and 100 gigabits per second. 3

Individuals and organizations also use wireless communication. The WiFi 4 standard in conjunction with the availability of license-free radio frequency bands led to the rapid proliferation of wireless local area networks in homes and offices. When away from the home or office, we often connect to the Internet at WiFi hotspots, public locations with Internet-connected WiFi radios. We also connect distant locations with wide-area wireless links when installing cable is impractical. And we can use satellite links to reach remote locations, but they are expensive and introduce a delay of about .24 seconds because of the distance the signal must travel. 5

Cellular telephone networks are also growing rapidly. There were 1,263 million cellular users in 2000, and that had increased to 2,168 five years later. 6 (The number of wired telephone lines fell from 979 million to 740 million during the same period). Cellular communication has improved with time, and, in developed nations, we are deploying third and even fourth generation technology, which is fast enough for many Internet applications.