Event ID 503: IO coalescing disk device … is about to be spun down

Windows Event ID Lookup: What Windows event IDs mean: 4625, 4624, 4740, 6008, 41, 7045, 1102 and 3,000 more, with Windows' own message text, the fields and what to check.

Look up a Windows event ID from Event Viewer, a SIEM alert or a log export: what it means, the fields it records, and what to check. Many IDs are used by more than one source (event 41 is both a Kernel-Power crash and a boot error), so every definition is shown, the one people usually mean first. The message text is Windows' own, read from the event providers of Windows 10.0.26200.0, 2026-10-28; the notes are ours, based on Microsoft's security auditing reference.