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I presume that by "MB" you're referring to the remaining free RAM that your PC has. If yes, then that's normal - it's the system moving some of the memory to the pagefile causing the high disk activity. Some references would tell the user the disable the page file - while this will address the disk issue, this may and will lead to worse problems down the road.
The safest solution (based on my experience - yes, I've tried disabling the pagefile before) is to install more RAM in your PC.
If my presumptions are wrong, then we would need more information.
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