RHEL5 issue
 

Just installed RHEL 5 on intel based machine with 3 ghz cpu 512 ram n sata disk with gnome gui.

Problem is CPU remain high above 80 if work on firefox or open other gui application like editor n Xorg consumes all CPU..

what the issue ?

Run the top application to see what is happening.
Have you checked memory use in the system monitor?
gfx can use up cpu unexpectedly - what graphics card? What driver? Are you using compositing?
Are you experiencing any discomfort from this effect? Slowdown?

What is the output of:
cat /proc/cpuinfo

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