What are all components are included in the kubectl top node command?

Question

Its not clear enough that how the kubectl top node command showing the resouce consumption Percentaage and what are all factors its considering.

For example, our nodesize of the nodepools having 2, CPU, 7 GB RAM. Out of that when I describe the node its showing only 4.6 GB is as allocatable.

So for what purpose this remaining 2.5 GB is used for and what are all the components using this reserverd cache memory?

Eventhough the allocatable memory is showing as 4.6 GB (out of 7 GB), when I run the "kubectl top node" command, its shwon as 3.8 GB is consumed (than means 82% of the allocatable memory 4.6).

So inorder to analyse the exact usage of the pods within the node, i calculated each pods request memory/usage memory (which is higher), and the sum is resulted to only 2.3GB usage. So its not getting in sync with the top node commands output, and still 1.5 GB is missing from the above calculation with respect the "kubectl top node" command output and this difference is coming in addition to the cached memory of 2.5GB alrady. So totally out of 7GB RAM, only usable memory is around ~3 GB and remaing ~4 GB is simply cached by AKS.

So would like to understand the following points in details

• For what purpose the the memory is cached - difference between Actual memory and Allocatable memory ie 7GB-4.6GB = 2.4GB

• What are the components calculated under "kubectl top node " command? its not only the pods consumption but what are all component.

• Eventhough the memory is cached already(the above 2.4GB) , Why again the nodes are showing additional memory usage (3.8GB) than the actual pods usage(2.3GB) That means, - Kubectl top node output - 3.8GB - sum of pods request/Usage memory- 2.3 GB - Why again this 1.5GB is added to the top node command?