Red Hat has previously indicated that Red Hat Enterprise Linux 4 would be based on version 2.6 of the Linux Kernel. A beta version of the product, released in September 2004, was based on the Linux 2.6 kernel. The current version, Enterprise Linux 3, supports some features of the 2.6 kernel, but its kernel core is based on version 2.4.
New security improvements will come in the form of SELinux - a Security Enhanced Linux that contains some of the features common in trusted operating systems, although it is not itself a trusted operating system. Be assured though that on the security front this is a pretty mean beast and something that security conscious enterprises should be interested in upgrading their systems to. SELinux has for some time been available with Fedora Core Linux, a related project, but now makes the move to the more production suitable platform of Enterprise Linux 4.