Lots of kernel customizations.
When I worked at CERN, the Atlas project was developing high performance network stacks with low level IP protocols, to be able to cope with the data throughput from the particle accelerator.
When I worked at CERN, the Atlas project was developing high performance network stacks with low level IP protocols, to be able to cope with the data throughput from the particle accelerator.
Maybe that's part of the answer, but you can run a custom kernel in probably any distro - no need to provide an entire distro from scratch for that. So there must be more to it.