After Window 8 upgrade system running very slow, Disk usage 100%

I had window 7 and I upgrade to window 8, I found my system running very very slow and on task manager disk usage is around 100%. I did following steps to resolved this issues, now disk usage is 5 to 10% when ideal.

• Press windows + R key 
• Select the option "Control Panel"  > "System and Security" > "System".
• Click on "Advanced system settings".
• Under performance, click on "Settings".
• Go to Advanced tab, Under Virtual memory, click on "Change".
• un-check "Automatically manage paging file size for all drives" check box.
• Select your windows drive (where OS is installed).
• Click on Custom size radio button.
• Set Initial size equivalent to your RAM size in MB. (ex; if 4 GB RAM then type 4000)
• Set Maximum size to twice of your RAM size in MB. (ex; if 4 GB RAM then 8000)
• Click on Set and Click on OK to close all window.