How does the operating system detect thrashing?

Answer 1

Thrashing is the result of not having enough RAM, so your PC must use a portion of the hard disk (Page File), as RAM. This is called "Virtual Memory".
When your PC is accessing the Page File, it is known as thrashing. While this in no way harms your system, it's not as fast as using true RAM. The only way to prevent this is to invest in more RAM. These days it's best to go with at least 1GB.
Some people might suggest "memory optimizers" you could use, or tweaks that you can use to force your system to keep the kernel (core of the operating system) running in memory instead of using the Page File, I would avoid these. Check here:
http://www.tweakhound.com/xp/xptweaks/supertweaks11.htm

Look under "Memory optimizers" and " Disable Paging of Kernel".

Here's some more on the Page File and how to optimize it.
http://www.petri.co.il/pagefile_optimization.htm

Answer 2

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Thrashing is the process, where the process selected for execution is swapped out by another high priority process, before the first one uses any of the system resources.

I am not sure about how the OS detects it. My guess is that, whenever a new process is loaded for execution, the OS may note the time and also note at what time the process get swapped out.

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Vasu M
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