The good news inside of the Red Hat Enterprise Linux 5 distribution is that not only is the number of sub-products smaller, but whatever level you choose, you get aggressive support for advanced hardware. RHEL5 now follows two main branches, server and client, and is then delineated by CPU family.
A long list of CPUs is supported, but most importantly, multicore x86 64-bit CPU support is in the kernel. In our sampling, we found that RHEL5 correctly identifies processor family and feature set, as well as the number of cores supported. This translates to the capacity to use CPU features such as hyperthreading effectively, along with other features such as CPU/session partitioning and high computational needs.
As an example, multicore CPU servers that run RHEL5's Xen paravirtualization scheme can benefit from the ability to utilize the extra cores found in both Intel's Xeon and Itanium, and AMD's Sempron and Athlon CPU families. This allows load distribution where it hasn't been possible or predictable before. Multicore support also can translate to healthier database, rendering, and HTTP (and associated application) support.
Want Xen virtualization? Go x86-64.
If Xen is deployed, 32-bit machines are out of the question except for experimental purposes. Machines that support hyperthreading in the 64-bit models are needed for two reasons: thread domination potential, to allow more than one thread; and the 64-bit memory model permits gargantuan amounts of DRAM/DDR memory without having to resort to 32-bit memory paging schemes. A raft of servers has emerged that have space for 12GB and 16GB of memory, and motherboards are in design that go far above that number to support huge memory models, and memory-based execution schemes.
Xen and memory
For now, follow the example of Xen pioneers running Fedora and SUSE, and plan on at least 256MB of additional RAM per virtual machine that you will be running. Xen's own memory and CPU overhead is low, but you will need to pay attention to memory budgets for your virtual machines.
Red Hat also now supports an install-time selection of an iSCSI initiator, which enables the operating system to utilize the virtualized hardware storage support of an externally hosted iSCSI target system, and the resources in terms of disk storage behind the target system. This allows applications to get inexpensive connections to outside storage without the need for storage-area network (SAN) infrastructure. This adds to software RAID capabilities, as well as increasing support for fiber channel host bus adapters -- and therefore SANs. Paravitualized hosts can use minimal local disk system resources, while being supplied by external (and perhaps fortified) disk subsystem resources and even SCSI tape arrays/jukeboxes.
We found in testing that iSCSI at boot can mean very low local disk resources are needed, although if they're available, the opposite need can be fulfilled by using supplied autofs, which serves as an external file system cache that's easily managed.
On the client side, RHEL5 still supports GNOME primarily, and adds support for high-end graphics cards from popular vendors such as nVidia, ATI and others. Red Hat also adds AIGLX support, designed to accelerate the foundational graphics support of the RHEL5 client set. Although this doesn't translate into instant eye candy, users of popular GIS systems and video editors may get a boost if their applications support OpenGL.
RHEL5 is not an "eye candy" distribution like Novell's SUSE Linux Enterprise Desktop, Mac OS X or Windows Vista. Experienced Linux users avoid running X on servers, so it shouldn't be necessary to take the risk of proprietary graphics drivers on production systems.
In all, Red Hat's focus has been largely towards the goals of user-session controls and virtualization. Now, more than ever, the benefits of Red Hat Network support for the almost ghastly wide variety of both kernel, supported application and driver support will become more critical, and the crux of the value added by Red Hat's support services.