Different types of kernel packages in Red Hat Enterprise Linux

Red Hat provides many kernel packages, each with different capabilities. Installing an unsuitable kernel may prevent the system from recognizing all its hardware. For example, if a machine has 16 GB of RAM but you install 32-bit Red Hat with the standard kernel, the system will see only 4 GB. Choosing the correct kernel lets the system operate at its full capacity. The details and capabilities of each kernel type are as follows:

• kernel - Contains the standard kernel:
  • Supports 1 CPU.
  • Supports one multiprocessor configuration for Intel EM64T systems in Red Hat Enterprise Linux 3 only.
  • Supports up to 4 GB of RAM on 32-bit or x86 systems.
• kernel-BOOT - Contains the installation kernel (x86 only).
  • Supports 1 CPU.
• kernel-{*-}devel - Contains kernel header files, replacing kernel-source.
• Kernel-header - Contains the kernel’s C header files.
• kernel-debug - Contains the kernel with additional debugging options. Available only in Red Hat Enterprise Linux 5.
• kernel-doc - Contains kernel documentation in /usr/src/linux{-*}/Documentation.
• kernel-hugemem - An additional kernel in the kernel-smp family (multiprocessor support), available only for 32-bit or x86:
  • 4 GB/4 GB split: 4 GB for the kernel and 4 GB for user processes. Normally, 32-bit systems divide memory into 1 GB for the kernel and 3 GB for user processes.
  • Requires more than 16 GB of RAM.
  • Supports up to 64 GB of RAM.
  • Not available in Red Hat Enterprise Linux 5.
• kernel-PAE - A kernel supporting up to 16 GB of RAM, available only in 32-bit (x86) Red Hat Enterprise Linux 5.
• kernel-smp - in addition to the options of kernel:
  • Supports multiprocessor systems, or more than 1 CPU. (Hint: in older Linux versions, machines with more than one CPU need this kernel. With the standard kernel, Linux sees only 1 CPU.)
  • PAE, or Physical Address Extension (for x86), supports up to 16 GB of RAM.
• kernel-pcmcia-cs - A kernel supporting PCMCIA cards.
• kernel-source - Contains the kernel source code.
• kernel-utils - Contains utilities for controlling the kernel or system hardware.
• kernel-xenU - The kernel for paravirtualized guest operating systems in Xen.
• kernel-xen - A kernel used for a Xen host (virtual machine). Its architecture variants depend on whether you install a 32-bit, 64-bit, or Intel Itanium (64-bit) kernel. Their details are:
  • 32-bit or x86:
    • Supports up to 16 GB of RAM.
    • Supports up to 16 CPUs.
  • 64-bit or AMD64, Intel 64:
    • Supports up to 1 TB of RAM.
    • RHEL5.0 and 5.1 support up to 32 CPUs.
    • RHEL5.2 supports up to 64 CPUs.
    • RHEL5.3 supports up to 126 CPUs.
    • RHEL5.4 and 5.5 support up to 192 CPUs.
  • Intel Itanium
    • Supports up to 32 CPUs.
• kernel-{*-}unsupported - A kernel that Red Hat does not support. You must resolve any problems yourself, even if you have a support subscription.

Reference: Red Hat