RAM in Ubuntu vs Other OS

My brother has a Thinkpad Lenovo X220s (Quad Core i5 and 8gb RAM) and it was super slow and laggy running windows 7. So I decided to put Ubuntu on it for him and ever since then it has been running great, better than the Windows OS ever ran (he only uses the computer for general purposes). Recently, I noticed that when he is using Ubuntu he had around 7gb of ram free compared to 2 free ram gb when using Windows. So my question is: Is the ram usage actually lower on Ubuntu and so if someone buys an 8gb ram computer and run ubuntu on it, then they would be having the equivalent ram of a 16gb ram computer running windows?. Moreover, how do different OS's handle RAM, ie is 8gb on MacOS gonna give you the equivalent of more or less ram than 8gb on a typical windows machine of similar price (think 8gb Ram on the M1 Mac Book Pro vs 8gb Ram on the Dell Laptops that go for ~$1500 and run Windows vs 8gb Ram on the same dell computer but with Ubuntu).

Thanks and have a good day!

Solution 1:

Ram usage on Ubuntu is lower than Windows. It has much less background processes and Gnome (The desktop environment) while using more ram than other desktop environments uses much less ram than Windows desktop environment does.