And which Linux kernel did you run, surely not 2.4.2?

• We've long run custom kernels and maintained our own kernel source.

• Drivers for our custom hardware

• Oh look, we got a dump truck of really cheap RAM, but not all the bits are usable. Can we work around the bad RAM cells in software and use it anyway?

• Hardware or kernel bugs that only showed up with many machines (we do upstream such changes)

• Custom memory management and containers before they were available in the mainstream kernel.

• We do reboot machines in staggered fashion for kernel updates.