How much RAM can 64-bit use?

Could you please clarify for me, just how much RAM can a 64-bit system effectively utilize? I'm curious to know the upper limit of memory that a 64-bit architecture can handle, as I'm considering upgrading my system and want to ensure that I make the most of the potential benefits of a 64-bit operating system. Is there a specific amount of RAM that's recommended for optimal performance, or is the sky really the limit when it comes to memory utilization in a 64-bit environment? I'd appreciate any insights you can provide on this topic.