RHEL5 won't install on Dell OptiPlex 745 with more than 4G RAM

I wanted to install RHEL5 x86_64 on a Dell OptiPlex 745 (that's an Intel Q965 (ICH8) Express chipset). I had a spare one sitting around and it had 6G of RAM.

However, when I booted from the installer CD and chose the RHEL 5 Server x86_64 option, it got up to the initrd line and then lots of text started scrolling by. The text was hard to read but I could make out the following phrases:

• mapcount

• trying to fix it up, but a reboot is needed

After letting that scroll by for a while, I ended up with a message stating that there was a kernel panic.

I was frustrated at not even being able to run the installer, but I solved this by passing the following parameters to the kernel:

I then hopefully updated the box to kernel-2.6.18-128.4.1.el5.x86_64.rpm but alas, the same problem returned at boot time.

Finally, I pulled two 1G sticks from the box, reducing the memory to 4G. Now it boots fine.