The computer itself is the simulation and so there is no need for an additional 'outside our universe' computer, but rather a platform of rules for the computer to operate. Also, keep in mind that a computer doesn't need hardware, just 1's and 0's.
The human mind cannot comprehend infinite time or space and so we should inherently know that much of the reason and functionality of our existence is incomprehensible and even unfathomable to our small human minds.
Everyone should read God's Debris by Scott Adams
I've studied AI stuff for a few years now and my view on reality is constantly evolving the more I learn...
I am under the impression that everything in our existence, broken down to its simplest form, is nothing but a series of facts (observed or otherwise unknown to us) in specific patterns. These patterns of facts, glued together to form data trees, comprise all of reality.
Its like all of matter is one giant glob of putty, constantly churning, forming new random facts and data patterns. Much like how matter is neither destroyed or created; it is recycled.
Reminds me of a recent article
about Horizontal Gene Transfer.
We are all just subsystems of a bigger dataset and there is no real individualism.