How Much Bandwidth is Enough? A Tbps!

by Jakob Nielsen on November 1, 1995

These days, websurfers dream of their own, personal, T1 line  but when I pick up my New York Times from the driveway Sunday morning, I am bringing information into my house at ten times T1 speed. In the long term we will need about a million times more bandwidth than a T1, as shown by the following list of requirements for the perfect user interface:

OK Audio: CD-quality sound at 150 kilobytes per second is all we need to achieve concert-hall quality. OK, some audiophiles claim that they can tell a small difference between CD recordings and reality, but 300 KB/s is probably the absolute max anybody would need for perfect stereo sound. Some interfaces may use 3-D "surround-sound", but the bandwidth requirements should be the same, even if the playback devices and the signal processing might differ.
OK Color: 24-bit "truecolor" monitors are sufficient since they show millions more shades of color than the human eye can discriminate.
Bad Resolution: Current computer screens typically use around 80 dpi (dots per inch) resolution which is horribly low and one of the main reasons that reading from screens is about 25 percent slower than reading from paper. Screens with a laser-printer-like resolution of 300 dpi have already been invented, but optimal user interface quality will require typeset quality of about 1200 dpi.
Bad Screen size: A typical big monitor is about 1024x1024 pixels these days. Increasing screen resolution to 300 dpi implies a 4096x4096 monitor if we are satisfied with the same amount of screen real estate. Of course, even a "big" monitor is much smaller than, say, a newspaper spread, so we need monitors to be at least three times wider and two times taller, or 12Kx8K pixels in 300 dpi resolution. Given that we want 1200 dpi resolution, we can conclude that monitors should display 48Kx32K pixels.
Bad Scan rate: Refresh rates of 60 frames per second are sufficient to minimize flicker on the conscious level, but we really need at least 120 frames per second for perfect image quality.
Bad CPU speed: Computers are much too slow to support real-time transformations of the kind of data we want for the perfect user interface. I know of customers who use a SPARCcenter 2000 as a personal computer even though it is intended as a server for monster databases (we use one to support the entire Internet community's access to Sun's website). These users are willing to pay what it takes to get maximum computer power because they need to analyze and manipulate large amounts of satellite imagery. Even faster computers will be needed for future applications.

A 48Kx32K pixel monitor with 24-bit-per-pixel color needs 4.6 GB videoRAM, so it will probably be about seventeen years before these perfect monitors are commonplace. Given a refresh rate of 120 fps, a 4.6 GB screen will require about four tera bits per second bandwidth without compression, or one Tbps with some compression.

The above analysis has shown that a one Tbps connection will suffice to support the computer display we want from a human factors perspective. One trillion bits per second might currently seem like an excessive bandwidth for a single user, and it is certainly true that most users will not need their entire screen driven by Internet full-quality video all the time. On the other hand, many user interface designs require more, not less, bandwidth since computers will need to download more information than the users see displayed on their screens: the only way to cope with information overload is to download even more data and use information filtering to decide what parts to bring to the user's attention.

We can draw a very pragmatic conclusion from this analysis: we are not going to have sufficient bandwidth any time soon. Thus, any development of new WWW software and any design of new websites must be done under the assumption that bandwidth is a precious resource that needs to be conserved.


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