The world produces between 1 and 2 exabytes of unique information per
year, which is roughly 250 megabytes for every man, woman, and child on
earth. An exabyte is a billion gigabytes, or 1018 bytes. Printed
documents of all kinds comprise only .003% of the total. Magnetic storage
is by far the largest medium for storing information and is the most rapidly
growing, with shipped hard drive capacity doubling every year. Magnetic
storage is rapidly becoming the universal medium
for information storage.
The cost of magnetic storage is dropping rapidly; as of Fall 2000 a gigabyte
of storage costs less than $10 and it is predicted that this cost will drop
to $1 by 2005. Soon it will be technologically possible for an average person
to access virtually all recorded information. The natural question then
becomes: how much information is there to store? If we wanted to store "everything,"
how much storage would it take?
We have conducted a study to answer this question. In particular, we have
estimated yearly US and world production of originals and copies for the
most common forms of information media. We have also attempted to estimate
the cumulated stock of information in various formats. Finally, we have
described the magnitudes of some communication flows that are currently
not stored but may well be in the future.
Information produced by medium
Most information is stored in four physical media: paper, film, optical
(CDs and DVDs), and magnetic. There are very good data for the worldwide
production of each storage medium, and there are reasonably good estimates
of how much original content is produced in each of these different formats.
We have identified production of content by media type, translated the
volume of original content into a common standard (terabytes), determined
how much storage each type takes under certain assumptions about compression,
attempted to adjust for duplication of content, and added up to get total
Table 1 depicts yearly worldwide production of original
stored content as of 1999. In general, the upper estimate is based on
the raw data, while the lower estimate reflects an attempt to adjust for
duplication and compression. We discuss these adjustments below and in
the medium-specific documents. Note that the growth rate estimates are
very rough. See the "Qualifications" section
and Appendix A for further discussion; the details
of the calculations are presented in the accompanying documents.
1: Worldwide production of original content, stored digitally using
standard compression methods, in terabytes circa 1999.
Type of Content
Three striking facts emerge from these estimates. The first is the "paucity
of print." Printed material of all kinds makes up less than .003
percent of the total storage of information. This doesn't imply that print
is insignificant. Quite the contrary: it simply means that the written
word is an extremely efficient way to convey information.
The second striking
fact is the ``democratization of data.'' A vast amount of unique information
is created and stored by individuals. Original documents created by office
workers are more than 80% of all original paper documents, while photographs
and X-rays together are 99% of all original film documents. Camcorder
tapes are also a significant fraction of total magnetic tape storage of
unique content, with digital tapes being used primarily for backup copies
of material on magnetic drives.
As for hard drives, roughly 55% of the total are installed in single-user
desktop computers. Of course, much of the content on individual users'
hard drives is not unique, which accounts for the large difference between
the upper and lower bounds for magnetic storage. However, as more and
more image data moves onto hard drives, we expect to see the amount of
digital content produced by individuals stored on hard drives increase
This democratization of data is quite remarkable. A century ago the average
person could only create and access a small amount of information. Now,
ordinary people not only have access to huge amounts of data, but are
also able to create gigabytes of data themselves and, potentially, publish
it to the world via the Internet, if they choose to do so.
The third interesting finding is the "dominance of digital"
content. Not only is digital information production the largest in total,
it is also the most rapidly growing. While unique content on print and
film are hardly growing at all, optical and digital magnetic storage shipments
are doubling each year. Even today, most textual information is "born
digital,'' and within a few years this will be true for images as well.
Digital information is inexpensive to copy and distribute, is searchable,
and is malleable. Thus the trend towards democratization of data---especially
in digital form---is likely to continue.
It goes without saying that the numbers in Table 1 can only be taken as
rough estimates. We have had to make various assumptions in order to construct
our these figures, and some data sources are contradictory or simply not
available. Here we list some of the most serious methodological qualifications,
each of which offers interesting challenges for those who would seek to
refine these estimates.
It is very difficult to distinguish "copies" from "original"
information. A newspaper, for example, is published on paper, often
published on the Web as well, and is generally archived on microfilm.
In fact, most printed materials are produced and/or archived magnetically.
There is also lot of duplication within each medium: many newspapers
reproduce stock prices, wire stories, advertisements and so on. Ideally,
we would like to measure the storage required for the unique
content in the newspaper, but it is very hard to measure that number.
As indicated above, the duplication issue is particularly serious for
digital storage, since little of what is stored on individual hard drives
is unique. We've tried to adjust for this the best we can, and documented
our assumptions in the detailed treatment of each medium.
Unlike print or film, there is no unambiguous way to measure the size
of digital information. A 600 dot per inch scanned digital image of
text can be compressed to about one hundredth of its original size.
A DVD version of a movie can be 1000 times smaller than the original
digital image. We've made what we thought were sensible choices with
respect to compression, steering a middle course between the high estimate
(based on ``reasonable'' compression) and the low estimate (based on
highly compressed content). It is worth noting that the fact that digital
storage can be compressed to different degrees depending on needs is
a significant advantage for digital over analog storage.
Should information stored as "backup" be included in the
total? This question arises for microfilm, rewritable CD ROMS, and even
with print, but digital magnetic tape is the most difficult case. Tape's
most common use is to archive material on hard drives and therefore
should not count towards the stock of ``original information'' produced
each year. Industry rules of thumb suggest that there is about 10 times
as much storage on tape as on hard drives. This fraction has been falling
as more and more data is stored on arrays of hard drives, which are
much more convenient to use. We've omitted most tape storage for this
reason. However, we should also note that vast quantities of original
scientific data are stored in tape libraries; we describe a few such
repositories in the detailed treatment of magnetic storage.
World and US production.
The US produces about 25% of all textual information and about 30% of
the photographic information, a significant fraction of the world's
total. We don't have good data on magnetic storage, but it seems plausible
that the US produces at least half of the content stored on magnetic
media. We've used numbers for world production when available, but in
some cases have had to extrapolate from US production. Little data is
available about information production in the Third World.
The production of unique content in books, photos, and CDs is barely
growing. DVD content is growing rapidly, but that's because it is a
new medium and a significant amount of legacy content is being converted.
By contrast, shipments of digital magnetic storage are essentially doubling
TV and Radio.
Original TV content produced each year is generally stored on magnetic
camcorder tapes, and so is counted in that category of storage media.
Much radio content is simply broadcast music, which we have already
captured with the CD statistics. See Table 3 for information on how
much storage it would take to back up all TV and radio broadcasts, with
minimal adjustment for duplication.
Our project is primarily concerned with content that is stored, either by
institutions or by individuals. But there is a lot of material that is communicated,
without being systematically stored. Some of this material is born digital,
such as email, Usenet, and the Web. Some of it is non-digital, such as telephone
calls and letters.
We expect that digital communications will be systematically archived in
the near future, and thus will contribute to the demand for storage. Table
2 shows how much storage would be required to archive the major forms of
2: Summary of yearly unique computer-mediated information flows.
In 2000 the World Wide
Web consisted of about 21 terabytes of static HTML pages, and is growing
at a rate of 100% per year. Many Web pages are generated on-the-fly from
data in databases, so the total size of the "deep Web" is considerably
Although the social impact of the Web has been phenomenal, about 500 times
as much email is being produced per year as the stock of Web pages. It appears
that about 610 billion emails are sent per year, compared to 2.1 billion
static Web pages. Even the yearly flow of Usenet news is more than 3 times
the stock of Web pages. As Odlyzko (2000) puts it,
"communication, not content, is the killer app."
We also estimated the storage requirements if one attempted to archive all
the non-digital communication flows in the United States. We consider only
the US since we didn't have very good data for worldwide communication.
The results are shown in Table 3.
3: Summary of yearly non-digital communication flows in the United
The striking thing here
is the volume of voice telephone traffic, most of which is presumably unique
content. Radio and TV, by contrast, have a huge amount of duplication from
station to station, since many of the broadcasts are reusing the same content.
Consumption of Information
Though the main focus of our report is on the supply of information, it
is interesting to look at data measuring the consumption of information
as well. Table 4 depicts hours per year of time spent
on various media in US households in 1992 and in 2000. We do not have good
data on information use in the workplace.
4: Summary of yearly media use by US households in hours per year,
with estimated megabyte equivalent. (Hours from Statistical Abstract
of the United States, 1999, Table 920, (projected)).
The notable features
of this table are 1) the hours spent on TV and radio consumption and their
consistency over time; 2) the reduction in time spent on printed information;
and, 3) the dramatic increase in home video, video games, and Internet usage.
However, it is important to note that the latter three categories are still
very small in terms of total hours.
It is also noteworthy that total time spent in media access has hardly changed
in eight years. Even while information supply is growing dramatically (especially
in electronic media) the actual consumption of information is barely changing:
a smaller and smaller fraction of what is produced is actually consumed,
on average, a trend noted by Pool (1984). Census data
indicate that over 40% of the US population has access to the Internet,
so this trend is likely to increase.
Individual and Published Information
We remarked above that technological advances have allowed for a "democratization
of data:" individuals can now generate a huge amount of information
on their own. Table 5 summarizes the yearly production
of information by and about individuals.
5: Yearly production of individual information
million installed drives
The production of individual
information can be compared to the amount of "published" information
in Table 6. Note that the amount of "individual"
information is over 2,600 times larger thanthe amount of published information.
Although the Web, Usenet, and email include a great deal of individual information,
they have been omitted from both of these tables, since it is difficult
to know whether to classify this material as "individual" or "public."
In the future we expect the distinction between "individual" and
"public" to become increasingly blurred.
6: Yearly production of published information
The world's total
production of information amounts to about 250 megabytes for each man,
woman, and child on earth. It is clear that we are all drowning in a sea
of information. The challenge is to learn to swim in that sea, rather
than drown in it. Better
understanding and better tools are desperately needed if we are to take
full advantage of the ever-increasing supply of information described
in this report.
About this Report
for this study was provided by EMC. We
view this report as a "living document" and intend to revise
it based on comments, corrections, and suggestions. Please send such materials
About the School of Information Management and
UC Berkeley's School
of Information Management and Systems is the first school in the nation
to explicitly address the growing need to manage information more effectively.
With respect to education,
we are training a new type of professional: "information managers".
Our graduates are familiar with the latest and most powerful techniques
for locating, organizing, retrieving, manipulating, protecting, and presenting
information. They study not only technology, but also the institutional,
legal, economic and organizational factors necessary for creating information
systems that meet peoples' needs.
With respect to research,
we are examining ways to build more effective tools and systems for managing
information. This effort is inherently multidisciplinary, involving computer
science, information science, social science, cognitive science, and legal
- A. Powers of Ten
The Powers of Ten table is helpful in
illustrating the relative size of gigabytes, terabytes, petabytes and
- B. Upper and lower estimates
The upper estimate is a reasonably "hard" number; based on
published data. The lower estimate is an attempt to adjust for duplication
and compression. Here is a quick summary of some of those adjustments.
There is some duplication with ISBN numbers due to paperback, hardback,
different editions, etc. There is duplication with financial papers,
ads, and so on in newspapers. We used CPC compression, which captures
images; conversion to ASCII eliminates images, but compresses text
If we used JPEG compression, rather than PhotoCD, we get a much
smaller number for the storage requirements for images.
- Music CDs.
If we use MP3 compression we get a much smaller number for the storage
requirements of audio files.
We assume that about 20 percent of magnetic storage is unique.
- C. Reading the data
The left-side navigation and Site Map provide
links to summary reports on each medium. The summaries provide links
to detailed reports and spreadsheets containing the raw data.
Within each media type, we have distinguished between originals and
copies, and between the yearly flow of production and the accumulated
stock. We've also described growth rates and compression issues for
- D. Acknowledgements
Gray and Shenoy (2000) provides useful information
on trends in magnetic storage. Lesk (1997) conducted
an earlier study that attempted to estimate the total stock of information.
Pool (1984) examined the flow of information in
the US circa 1980. See the individual
acknowledgements for the names of people who helped us.
- Jim Gray and Prashant Shenoy.
Rules of thumb in data engineering.
in Proceedings of 16th International Conference on Data Engineering,
pages 3-12. IEEE, 2000.
- Michael Lesk.
How much information is there in the world?
Technical report, lesk.com, 1997.
- Andrew Odlyzko.
Content is not king.
Technical report, AT&T Labs, 2000.
- Ithiel De Sola Pool, Hiroshi Inose, Nozomu Takasaki, Roger Hurwitz.
Communications flows : a census in the United States and Japan.
Elsevier Science, New York, 1984.
- Ithiel De Sola Pool. "Tracking the Flow of Information".
Science (12 August), 1983, 221:4611, 609-613.
- U.S. Census Bureau.
Statistical Abstract of the United States, 1999
Washington, D.C., 1999.
© 2000 Regents
of the University of California