Dive into Systems is a free, online textbook that serves as a gentle introduction to computer systems, computer organization, and parallel computing. The book is intended for an audience that has only a CS1 background. It guides readers through a vertical slice of a computer to develop an understanding of a variety of systems topics, including:
how a computer runs a program, from a program expressed in a high-level language to low-level binary representation and circuits
programming in C and Assembly, assuming a CS1 background
introduction to operating systems and the systems costs that affect program performance (the memory hierarchy, caching, and code optimization)
introduction to parallel computing with shared memory and pthreads