Windows 10: Computer slow down after Memory usage than 4 GB Ram while playing

I notice that Computer slow down when ram reach at 4 - 5 GB ram out of 8 GB. I got old geforce gtx 650 ti. I am not really intense gamer. However, i can get more than 90 fps. i am not sure why is like that. Even as power user like me could n't figured out. Any help will be appreciable.

:)

 

Xbox DVR high ram usage

I've been playing Hearthstone and using the Xbox DVR to record in the background for those awesome moments. My main pc has no issues as it has 16 gb RAM, but I recently got a 4 gb RAM surface and started noticing some issues. RAM usage by Broadcast DVR server
skyrockets from the normal 500ish MB to 1000+ from time to time. I was wondering if it was just a lack of memory and after some investigating, I think I've narrowed it down to this:

On my surface whenever I alt-tab out of my game while the DVR server is running, everything becomes sluggish. When checking the RAM usage in Task Manager, it turns out memory usage is 97%+ due to the issue from above. Eventually the DVR server closes itself
(I suppose due to too much RAM usage).

So I tried it out on my laptop, RAM usage by the DVR server sits at 600ish MB. I have a dual monitor setup.
Whenever my mouse hovers outside of my monitor that is being used to play my full screen game/ any activity outside the game display, RAM usage starts climbing.
I saw it climb up to 4000+ MB! If I go back to the game or move the other window back to the main screen and use it on top of the full screen game, RAM eventually drops back down to 600ish MB.

My question is, why does this happen? And is there a fix so that I could do stuff on my second display without super high ram usage?

 

Antimalware Service Executable & Cortana Using Too much ram

My laptop has 64-Bit Operating System with 4 GB RAM. Most of the RAM is used by Antimalware Service Executable & Cortana which are 70 MB and 40 MB respectively. Usually RAM usage(Memory in Task Manager) is more than 40 % even if I am not using any software.
My friend said that RAM usage must be below 20 %. How to reduce this usage?

#sorryforenglish