Windows – Disk 0 (C:) missing from Task Manager Performance Tab in Windows 10

In Vista and later the Cached value is the sum of the Standby and Modified lists as shown in Resource Monitor. This is RAM. The CPU cache is internal to and managed by the CPU and not shown in Task Manager. The file cache is RAM used to contain frequently accessed portions of disk files. It is not part of the Cached value and Task Manager shows nothing about it.

The Standby list is RAM and serves a dual role. It contains application data but has not been recently accessed. In fact much of it will never be used by the application again. If it is later needed the application can quickly reclaim it.

The data in the Standby list is also on the disk. This makes it possible to quickly reassign this memory to any other process that needs it. The details are complex and I will not describe them here.

The Modified list is RAM that contains data that has not yet been saved to disk. When that is done it will go to the Standby list. It's size is usually quite small, probably less than 50 MB on a 4 GB system. I will say no more about it.

Most of the Cached value is available memory and freely available to any process. This is much better than free memory which should be kept to the absolute minimum.

Cached memory is a major contributor to system performance and a high value is a good thing. Clearing it would almost always be bad idea and would negatively effect performance. Windows provides no user accessible means of doing so. There are utilities available that can do this but they are best left to those who have a thorough understanding of the implications.

As a general rule caches are best left alone. They are complex and would not have been developed unless they provided a valuable service.

I see nothing in the screenshot that would be a cause for concern.

That main window combines the disk usage of the two as you said.

I't doesn't seem to care whether or not the other drive is being used and it will always base the percentage depending on how many drives you have. in my case i have 3 drives and thus the main window will judge each drive on a scale of 33% each. if only one drive is handling operations in that moment then 33% will be the max usage reported for that drive, if two then 66% etc.

this is the epitome of stupidity by Microsoft as common sense would have indicated a person uses the task manager for a more in depth analysis of what's going on with their system, combining the usage of our drives isn't the smartest move. also there is no option to select if you want it to show usage per disk or not