Red Hat Enterprise Linux v.4 based on Linux 2.6 kernel infrastructure

Linux v.4 kernel offers numerous improvements over earlier kernels, including many enhanced algorithms and features:

Generic logical CPU scheduler: Handles multi-core and hyperthreaded CPUs.

Object-based Reverse Mapping VM: Improved performance in memory constrained systems.

Read Copy Update: SMP algorithm optimization for operating system data structures.

Multiple I/O schedulers: Selectable based on the application environment.

Enhanced SMP & NUMA support: Improved performance and scalability for large servers.

Network interrupt mitigation (NAPI): Improved performance for heavy network loads.

Red Hat Enterprise Linux ES for Small and Midrange businesses

Databases - Leading open source databases: PostgreSQL, MySQL
Development - Environments for C, C++, Java, Fortran with Perl, Python, CVS and Emacs
Engineering - Computational tools including blas, pvm, and lam
File servers - FTP, NFS, and Samba (CIFS)
Mail server - IMAP/POP servers with Cyrus, Sendmail, spamassassin
Networking - Complete suite of network servers and firewall
Printing - CUPS/lpr printing systems
Security - Extensive features including SSL, IpSec, MAC/DAC
Web server - Apache server with numerous mod/php plugins

Linux Setup and Sustainence Tips

Getting Started

The word Linux, though it in its strictest form refers specifically to the kernel, is also widely and correctly to refer to an entire operating system built around the Linux kernel. It is a multitasking,multiuser,multiplatform,multiprocessor and multithreading OS.

One of the great features of Linux is the abundant choices. Linux technically refers to the operating system kernel but it's usually understood that when you refer to Linux you're referring to the kernel as well as the applications and supporting software that surround it.
The packaging of the kernel and various supporting software and applications composes what is called a distribution. There are many different Linux distributions.

Please refer to http://distrocenter.linux.com/ for more details.