Affymetrix Data Packages
The package 'affy' relies on environments to extract probe sets
from the CEL data.
The information concerning the probe locations on a chip
are extracted from the CDF files and stored in packages. This allows us
to have a mechanism to link the right CDF information directly from the
CEL file (and free the user from having to do it). This implementation also
reduces a bit the memory usage (not everything contained in CDF is
stored, only enough to know "what is where") and improves the performance
during lookups (speed). There are other advantages, which will be
revealed in time...
The packages must be installed after being
downloaded. You may want to refer to the FAQ to know more about how
to install a package if have a doubt.
All of the Bioconductor CDF packages are available in the middle
column of the main metadata page.