[co-operative vs. pre-emptive]
At different levels, distributed computing, parallel processing, or grid services [L1 ] are related topics.
developerWorks hosts a write-up of some of this material [L2 ]. While Jon Stokes' "Introduction to Multithreading, Superthreading and Hyperthreading" [L3 ] claims to be mostly about (rather specific) hardware, in fact its readability and confident accuracy recommend it for those in search of a more general introduction to operating system-level concurrency.
Tclonians typically focus on maintainability and related development issues. For a hard-core performance perspective on concurrency, see "The C10K problem" [L4 ].