When a computer freezes, why are we able to move the cursor around freely while everything else is frozen?

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When a computer freezes, why are we able to move the cursor around freely while everything else is frozen?

In: Technology
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In that scenario, the whole computer hasn’t frozen. Only some aspect — the User Interface, or some underlying service that the UI relies on.

Mouse events are typically interrupt-driven. That is, when the mouse is moved, the CPU is “interrupted” from whatever it was doing (such as the UI or system service being in a crashed state), moves the mouse cursor, then resumes whatever it was doing (going back to the UI/service being crashed).

In a “true” or total crash, you’ll lose the mouse cursor as well.

depends on the system. When a windows program that’s open in a window “stops responding”, it means that it has stopped translating, dispatching and receiving default [window messages](https://docs.microsoft.com/en-us/windows/win32/learnwin32/window-messages), such as “WM_PAINT” (redraw the window please), “WM_CLOSE” (close the window please) etc.

A lot of user interfaces work this way; with a constant “while loop” going on for as long as the UI element is alive; inside of that while loop the window’s message is received from the operating system or something else; it’s decoded and then something is done based on it.

Computers have different levels of operation. Way down at the bottom is the kernel, then the OS itself, then drivers, then various elements of interface control. If just all your screen widgets freeze up, it doesn’t mean everything else is frozen, and your mouse may still work because it’s run as a separate process.