Processes

concurrency is structure: many logical tasks in flight, interleaved on however many cpus you have (possibly one). parallelism is hardware: tasks literally executing at the same instant. a single-core machine juggling 400 socket connections is concurrent, not parallel; a gpu multiplying matrices is parallel, barely concurrent. you design concurrency; you buy parallelism (Tanenbaum, Andrew S., 2008).

threads and shared memory#

a thread is an independent stream of execution inside one address space: own stack and registers, shared everything else. the sharing is the point — and the disease.

unix is less an operating system than a worldview: everything is a file, every program does one thing, and text streams are the universal interface. linux is the worldview’s most successful implementation — a monolithic kernel started by a finnish undergraduate in 1991, now running most of the internet, every android phone, and the top 500 supercomputers without exception. 𐃏 this page is the trunk; the sharpened tools each get their own branch: