The type of storage in memory to store the data value according to the CLI standard specification basically falls into these three storage categories (from fastest to slowest):
Register
Stack
Heap
Register is the fastest to access, because it does not have memory allocation overheads compared to stack and heap. The concept of register is similar to the processor's register. This register is not the same as stack and heap; it is related to how the value is stored in the code. Usage of register in CLR is translated into any of the processor's registers, and depends on the platform used. For example, when running on x86/x64 processors, Intel's general purpose register of EAX, EBX, ECX, EDX will be used.