GC.Collect - how it really works - .net Garbage Collection

The GC (Garbage Collection) in .Net is a Win32 process within HEAP which is initially created by the OS (Operation System) based on CLR request. This request add 2 segments of 16 MB each (16kb committed). One of them is allocated for the Gen0, Gen1 & Gen2 and the second segment is used for LOH (Large Object Heap). Objects greater than 20 KBytes are treated as large objects by the Garbage Collector and are directly allocated in a special heap

While we start to create small objects the first segment starts to grow. If we suppose that we keep all instantiated objects without ever releasing any instance until the segment gets full, the CLR ask OS for another segment of 16MB (16kb committed) and continues to allocate object space from that new segment which has been received by the operating system.

If we free up memory, lets suppose all allocated 32 MB, CLR leaves you still with a HEAP size of 32 MB even that nothing is committed. The GC still held all free space and will not return it to the OS until we use a memory pressure.

With the memory pressure the operating system sending a signal to the CLR to trim the working set and the CLR will return additional segments to OS.

The conclusion of it is simple, there is plenty of free memory and the operating system does not claim anything from running processes.