Red Hat Inc.s Red Hat Enterprise Linux 4 stands as a leading example of how Linux and the constellation of open-source projects that surround it have grown capable of serving the needs of organizations, from the desktop to the server room. eWEEK Labs tests show that Version 4 of Red Hats flagship product is significantly more scalable and secure than previous versions, due in large part to its upgrade to Version 2.6 of the Linux kernel. Organizations that are running RHEL 3 now should test their applications with the new release to determine whether the performance gains theyll see are worth the disruption of an upgrade. (RHEL 4 is available for download at rhn.redhat.com for RHEL subscribers.)Two of the most important factors to consider when weighing the pros and cons of upgrading or migrating to a new operating system are the applications you wish to run and the hardware on which you intend to run them.If youre running commercial enterprise applications that support Linux, RHEL is the Linux distribution most likely to be certified for them. If youre looking to run applications in the open-source stack, RHEL is also a solid platform, featuring components that are up-to-date but that have had time to bake in Fedora, Red Hats community-supported Linux distribution. Click here for more on the RHEL vs. Fedora question. RHEL 4 also ships with compatibility libraries that enable it to run applications compiled for RHEL 2.1 and 3. Red Hat Desktop (as the desktop flavor of RHEL is known) makes a solid Linux client, but it doesnt do much to distinguish itself from the rest of the desktop Linux pack. Wed like to see Red Hat do more for desktop administrators by adding tools such as the user configuration management system in Sun Microsystems Inc.s Java Desktop System. The pricing for RHEL 4 is the same as that for Version 3: The server versions range from $349 for RHEL ES with basic support to $2,499 for RHEL AS with premium support. RHEL ES supports as many as two Intel Corp. x86, Itanium 2 or EM64T processors or up to two Advanced Micro Devices Inc. AMD64 processors. RHEL AS adds support for IBMs Power series (eServer iSeries and eServer pSeries) and mainframe (eServer zSeries and S/390) platforms, as well as support for significantly more processors. This breadth of platform support is one of RHEL 4s competitive advantages over the somewhat more parochial Solaris 10 and Windows Server 2003. Click here to read the review of Solaris 10. eWEEK Labs tested RHEL AS. Red Hat also sells a workstation version of RHEL, priced from $179 per system per year, as well as a corporate desktop version of RHEL, which, sold in packs of 50, costs about $70 per system per year. Red Hat Adopted the Linux 2.6 kernel for its enterprise line after the code had undergone a years worth of updates from the kernel development project, as well as broad testing in versions 2 and 3 of Red Hats community-supported Linux distribution, Fedora Core. (RHEL 4 ships with a kernel based on Linux 2.6.9.) One of the most significant improvements in the 2.6 kernel was to its disk I/O scheduler, which maximizes disk performance by sorting read-and-write requests and ensures that concurrently running applications get adequate access to the disk. With RHEL 4, we could select among four I/O scheduler options by passing an argument to the kernel at boot time. The noop scheduler, which is intended for use in virtualized environments, doesnt attempt to optimize at all, decreasing overhead by allowing the host operating system to worry about I/O optimization. The other three schedulers are anticipatory; deadline; and CFQ, or completely fair queueing (the default in RHEL 4). The schedulers handle disk I/O optimization differently, with each offering distinct benefits depending on the set of applications run. We were, therefore, disappointed to find that Red Hat does not discuss the relative merits of each option in its manuals. Nevertheless, we were able to find a good deal of information on this topic on the Linux kernel mailing list (at lkml.org). Linux 2.6 and, in turn, RHEL 4 also include a new process scheduler that scales better in multiprocessor, multicore and hyperthreaded CPU systems than does Version 2.4s process scheduler. Also of benefit to multiprocessor systems is the 2.6 kernels Read Copy Update feature, which speeds operations in which multiple processors need read access to particular data. Also courtesy of the new kernel is tremendous growth in the number of processors RHEL AS supports32 x86 processors (up from 16 in RHEL 3) or 64 Itanium 2 processors (up from eight in RHEL 3)as well as a lower-overhead virtual memory system and a block I/O file system that boosts the maximum size of RHEL 4s ext3 file system to 8TB. Next page: Tightened security.