The kernel image and ramdisk directory contains files that that must be loaded across the network to enable PXE booting of the ESX installer. vmlinuz is a Linux kernel used for booting. The kernel is located in the initrd.img file.

The kernel image and ramdisk directory is located on a Web server (for gPXE) or on the TFTP server in the /tftpboot directory (for PXELINUX without gPXE. For example, the directory might be at /tftpboot/esx/ and contain the following files:

-r--r--r-- 1 root root 1922578 Nov 12 05:51 initrd.img 
-r--r--r-- 1 root root 966633 Nov 12 05:51 vmlinuz

These files come from the ESX installation DVD, under the /isolinux directory.

You reference the vmlinuz and initrd.img files from the PXE configuration file. The following code snippet shows how you reference vmlinuz and initrd.img in the PXE configuration script:

kernel esx/vmlinuz
append initrd=esx/initrd.img ...
...