Windows 10: I have a 8Gb ram but sometimes my computer only boots up with 4 gb ram and somtimes with...

Can someone explain why does this keep happening?

:)

 

My PC was have 4 gb of ram i get 6 gb of ram and my pc is lagging what must i do when i buy 8gb of ram and wii be 9 gb of ram

My PC was have 4 gb of ram i get 6 gb of ram and my pc is lagging what must i do when i buy 8gb of ram and wii be 9 gb of ram

 

Not all ram usable in asus laptop with 8gb of ram usable 5.95 gb ryzen 3200U

UPDATE I took apart to see what is wrong and it looks like I have 4 gb of ram and I was supposed to have 8gb of ram and the system apparently recognisees as 8gb of dual channel ram

 

Only 4 of 8 gb ram available










Thanks for reading this post. I have a Dell Inspirion 5770 laptop. Screenshots of some pertinent specs attached. My task command prompt >systeminfo shows that I have 8,055 mb total physical memory installed but only 3,881 mb available physical memory. I have seached the web for solutions and have checked, under Windows search >Run > Msconfig > Boot > Advanced Options, I have left Maximum Memory unchecked. Since I have only 1 - 8gb ram stick, I cannot pull one stick out to see if the other is working. My question is: since I have 8gb ram installed, shouldn't I have, at least close, to 8gb of ram as "available physical memory"?
I use my laptop for computer graphic art and game development. So, my it is important that I make use of as much of my ram as possible.
Thank you, everyone for taking interest in my problem.