The software everything runs on.
WHAT IT IS
The software managing the machine and everything running on it.
WHAT THE COMMON ONES ARE
Windows, on most business computers macOS, on Apple computers Linux, on most servers and some desktops Android and iOS, on phones and tablets
WHAT IT DOES
Starts programs Manages files Handles devices Controls who may do what
WHAT VERSIONS MEAN
Each receives updates for a defined period, then stops.
WHY THAT MATTERS
A system no longer receiving updates is a permanent vulnerability.
WHAT TO CHECK
Which version you run, and whether it is still supported.
WHAT TO DO ABOUT AN UNSUPPORTED ONE
Upgrade, or replace the machine.
WHAT DIFFERS BETWEEN SYSTEMS
Where settings live What software runs File path conventions
WHAT DOES NOT
The concepts: files, folders, programs, permissions.
WHAT TO LEARN
Those concepts, which transfer between systems.
