The registry, NTFS, the security model, and the enterprise tooling behind Microsoft's OS.
Released August 24, 1995, Windows 95 brought the Start menu and taskbar to the mainstream — backed by one of the largest software marketing campaigns ever mounted, including a Rolling Stones-licensed ad and Jay Leno at the Redmond launch event.
How discretionary ACLs, mandatory integrity levels, and UAC's token-splitting combine to form Windows' layered access control model.
How WinRM and PowerShell Remoting turn scattered single-machine administration into fleet-wide scripted management.
How the Windows kernel represents processes as containers of handles and a security token, and the tools to inspect both live.
How Group Policy Objects, ADMX templates, and the client-side refresh cycle turn Active Directory structure into enforced machine configuration.
How Task Scheduler's triggers, actions, and conditions work together, and how to build and inspect scheduled tasks from the command line.
How the Service Control Manager starts, stops, and supervises background processes, and how to configure and debug a service directly.
How NTFS's Master File Table, transaction journal, and lesser-known features like alternate data streams actually work.
How a modern Windows machine goes from firmware to a running kernel, and where each stage's configuration actually lives.
How the registry's hive files, keys, and value types work under the hood, and the tools to inspect and edit them safely.