Restricted to computer science majors. An introduction to computer systems software abstractions with an emphasis on the connection of these abstractions to underlying computer hardware. Key abstractions include threads, virtual memory, protection, and I/O. Requires writing of synchronized multithreaded programs and pieces of an operating system. Four lecture hours and two discussion hours a week for one semester. Computer Science 439 and 439H may not both be counted. Prerequisite: Computer Science 429, or 429H with a grade of at least C-.