Why IE has 1.4GB memory limit?

I am developing a ActiveX control in IE.

The Activex can load several thousands CT images (512x512x16bit).

1000 images takes about 500MB.

I found that the memory of IE can only reach to 1.4GB. 

The ActiveX failed to allocate more memory, malloc() failed when request memory.

Windows 2008 R2 standard

16GB memory, more than 10GB memory are free.

32bit iexplorer.exe