The limit is usually address space fragmentation and at one point not being able to find a piece of memory large enough for an allocation. Depending on the allocation patterns this may happen around 3 GiB but for some applications even around 1.7 GiB already. VS gets unbearably slow around 2 GiB memory, though, most likely because the native allocator has to piece together all free pieces of memory again and in the managed part the GC probably has fun trying to compact memory.