High-level programming languages often conceal low-level system details from developers. However, certain tasks require a deeper understanding of these details, especially when it comes to efficient input-output for local file systems and networking. In this talk, Vitaly will explore computer architecture and operating system internals to shed light on what happens behind the scenes during input-output operations. He will examine three key perspectives: direct communication with I/O devices, interfaces provided by operating systems, and interfaces in functional programming languages, with examples from Scala, Haskell, and OCaml. The first perspective will reveal the foundations of asynchronous programming, while the other two will assist attendees in choosing the most suitable approach for implementing I/O in their own code.