Next: Compiling NEMO on HECToR
Previous: Communication and I/O networks
The service nodes (i.e. login and I/O) run SUSE Linux. The compute
nodes run a lightweight Linux kernel called the Cray Linux Environment,
or CLE. CLE was formally known as Compute Node Linux (CNL) and some
documentation may still refer to this. CLE is essentially a stripped
down version of Linux (c.f. Blue Gene's compute node kernel, CNK). It
is designed to be extremely lightweight so as to limit the number of
interruptions from the operating system. The rationale is to keep the
compute nodes as uninterrupted by the operating system as possible by
outsourcing the usual operating system tasks to dedicated additional
hardware. The benefits of this are potentially excellent scalability up
to large task counts which should results in minimal variation of
application run time. The downside of this reduced kernel is that some
services which a small number of applications expect or rely on, e.g.
access to the X11 libraries, are not available on the compute nodes.