Systems running 32-bit versions of Windows cannot address more than how much total RAM?

Systems running 32-bit versions of Windows cannot address more than how much total RAM?

• 2GB
• 8GB
• 4GB
• 4MB 

EXPLANATION

 on a 32bit machine the maximum amount of memory usable is around 4GB. Actually, depending on the OS it might be less due to parts of the address space being reserved: On Windows you can only use 3.5GB for example. On 64bit you can indeed address 2^64 bytes of memory.