The unofficial 3.1 release consists of three CDs for the IA32 architecture.

OpenBSD31-i386-base.iso:
------------------------
 o The base files necessary to install the system
 o X, ports, src and srcsys (kernel) TAR files, containing the source code
 o OpenSSH in source form and binary for RedHAT (RPM), this isn't really
   needed for OpenBSD since it includes already.
 o Patches for all architectures supported by OpenBSD (from version 2.2)

OpenBSD31-i386-base-ipf.iso:
----------------------------
 o Contains IPF (http://www.ipfilter.org/)

OpenBSD31-i386-packages[1-2].iso:
----------------------------
   These CDs contain the binary packages for OpenBSD/i386. If you prefer
   the ports tree over installing binary packages you won't need 
   these CDs.