The Depths of Windows I/O (Part 2) — Synchronous and Asynchronous I/O: What OVERLAPPED Really Means (archived 2026-08-30)

Abstract

Part 2 of a series explaining Windows synchronous and asynchronous I/O (overlapped I/O) with diagrams. It covers what FILE_FLAG_OVERLAPPED means, the four ways completion is reported, the conditions under which supposedly-asynchronous I/O completes synchronously, how to cancel properly, and how it all maps onto .NET. Archived version of https://comcomponent.com/en/blog/windows-io-sync-async-overlapped/, as published on 2026-08-30. The live article is maintained and may change after this date. First published 2026-07-29.