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+Introduction
+============
+
+`Kraken <http://ccb.jhu.edu/software/kraken/>`__ is a taxonomic sequence
+classifier that assigns taxonomic labels to short DNA reads. It does
+this by examining the :math:`k`-mers within a read and querying a
+database with those :math:`k`-mers. This database contains a mapping of
+every :math:`k`-mer in
+`Kraken <http://ccb.jhu.edu/software/kraken/>`__'s genomic library to
+the lowest common ancestor (LCA) in a taxonomic tree of all genomes that
+contain that :math:`k`-mer. The set of LCA taxa that correspond to the
+:math:`k`-mers in a read are then analyzed to create a single taxonomic
+label for the read; this label can be any of the nodes in the taxonomic
+tree. `Kraken <http://ccb.jhu.edu/software/kraken/>`__ is designed to be
+rapid, sensitive, and highly precise. Our tests on various real and
+simulated data have shown
+`Kraken <http://ccb.jhu.edu/software/kraken/>`__ to have sensitivity
+slightly lower than Megablast with precision being slightly higher. On a
+set of simulated 100 bp reads,
+`Kraken <http://ccb.jhu.edu/software/kraken/>`__ processed over 1.3
+million reads per minute on a single core in normal operation, and over
+4.1 million reads per minute in quick operation.
+
+The latest released version of Kraken will be available at the `Kraken
+website <http://ccb.jhu.edu/software/kraken/>`__, and the latest updates
+to the Kraken source code are available at the `Kraken GitHub
+repository <https://github.com/DerrickWood/kraken>`__.
+
+If you use `Kraken <http://ccb.jhu.edu/software/kraken/>`__ in your
+research, please cite the `Kraken
+paper <http://genomebiology.com/2014/15/3/R46>`__. Thank you!
+
+System Requirements
+===================
+
+Note: Users concerned about the disk or memory requirements should read
+the paragraph about MiniKraken, below.
+
+-  **Disk space**: Construction of Kraken's standard database will
+   require at least 160 GB of disk space. Customized databases may
+   require more or less space. Disk space used is linearly proportional
+   to the number of distinct :math:`k`-mers; as of Feb. 2015, Kraken's
+   default database contains just under 6 billion (6e9) distinct
+   :math:`k`-mers.
+
+   In addition, the disk used to store the database should be
+   locally-attached storage. Storing the database on a network
+   filesystem (NFS) partition can cause Kraken's operation to be very
+   slow, or to be stopped completely. As NFS accesses are much slower
+   than local disk accesses, both preloading and database building will
+   be slowed by use of NFS.
+
+-  **Memory**: To run efficiently, Kraken requires enough free memory to
+   hold the database in RAM. While this can be accomplished using a
+   ramdisk, Kraken supplies a utility for loading the database into RAM
+   via the OS cache. The default database size is 75 GB (as of Feb.
+   2015), and so you will need at least that much RAM if you want to
+   build or run with the default database.
+
+-  **Dependencies**: Kraken currently makes extensive use of Linux
+   utilities such as sed, find, and wget. Many scripts are written using
+   the Bash shell, and the main scripts are written using Perl. Core
+   programs needed to build the database and run the classifier are
+   written in C++, and need to be compiled using g++. Multithreading is
+   handled using OpenMP. Downloads of NCBI data are performed by wget
+   and in some cases, by rsync. Most Linux systems that have any sort of
+   development package installed will have all of the above listed
+   programs and libraries available.
+
+   Finally, if you want to build your own database, you will need to
+   install the
+   `Jellyfish <http://www.cbcb.umd.edu/software/jellyfish/>`__
+   :math:`k`-mer counter. Note that Kraken only supports use of
+   Jellyfish version 1. Jellyfish version 2 is not yet compatible with
+   Kraken.
+
+-  **Network connectivity**: Kraken's standard database build and
+   download commands expect unfettered FTP and rsync access to the NCBI
+   FTP server. If you're working behind a proxy, you may need to set
+   certain environment variables (such as ``ftp_proxy`` or
+   ``RSYNC_PROXY``) in order to get these commands to work properly.
+
+-  **MiniKraken**: To allow users with low-memory computing environments
+   to use Kraken, we supply a reduced standard database that can be
+   downloaded from the Kraken web site. When Kraken is run with a
+   reduced database, we call it MiniKraken.
+
+   The database we make available is only 4 GB in size, and should run
+   well on computers with as little as 8 GB of RAM. Disk space required
+   for this database is also only 4 GB.
+
+