I performed a clean installation of Mavericks yesterday and since then Kernel task takes up to 600-650mb of ram and firefox about the same amount of ram. Is there a way that I can fix this and what is the cause of this high ram usage?
What makes you think that the memory usage for the kernel task and Firefox is not normal? And how much system memory does you new iMac have? The standard memory configuration for a new iMac 27" model is 8 GB.
Right now as I'm typing this, my memory usage kernel task is 1.05 GB and Safari is using over 150 MB. Keep in mind that memory usage of any browser will increase as more web pages are opened. In any event, your memory usage seems normal to me.
Those numbers are not all that high, especially if you have a significant amount of memory (4+ GB). I wouldn't worry about that despite how high it might appear.
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