The Managed Heap

.NET components aren’t allocated off the raw memory maintained by the underlying operating system. Instead, in each physical process that hosts .NET, the .NET runtime pre-allocates a special heap called the managed heap. This heap is used like traditional operating system heaps: to allocate memory for objects and data storage. Every time a .NET developer uses the new operator on a class:

    MyClass obj = new MyClass();

.NET allocates memory off the managed heap .

The managed heap is just a long strip of memory. .NET maintains a pointer to the next available address in the managed heap. When .NET is asked to create a new object, it allocates the required space for the object and advances the pointer, as you can see in Figure 4-1. (Figure 4-1 is adapted with permission from Figure 1 in “Garbage Collection: Automatic Memory Management in the Microsoft .NET Framework,” by Jeffrey Richter (MSDN Magazine, November 2000.)

The managed heap

Figure 4-1. The managed heap

This allocation method is orders of magnitude faster than raw memory allocation. In unmanaged environments such as C++, objects are allocated off the native operating system heap. The operating system manages its memory by using a linked list of available blocks of memory. Each time the operating system has to allocate memory, it traverses that list looking for a big enough block. After a while, the memory can get fragmented, and consequently the list of available blocks gets very long. Memory fragmentation is a major source of performance problems because of the time it takes to traverse the list for allocation requests, combined with added memory page faults and disk access penalties.

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