Currently it is possible to have up to 2.1 billion rows in a Dot Net array, which is the array limit in Dot Net 4.5.
In Dot Net 4.0 there is a 2 GB limit per object.
32 and 64 bit operating environments are supported, although a 64 bit environment is recommended for scalability.
32 bit Dot Net environments are limited to 1.4 GB usable memory. In a 64 bit environment, as much memory as is available may be used. Also 64 bit environments have a much bigger virtual page space. This allows memory to be reallocated more efficiently, thus helping scalability.
In short, a 64 bit environment with Dot Net 4.5 is recommended for maximum scalability.
GCAllowLargeObjectSupport should be enabled in the .config file to allow for objects bigger than 2 GB.