Q:

What is the difference between BigInt and "Computer Algebra System" integers?

Obviously I imagine a CAS does more than BigInt does. But I'm wondering if there is a difference in implementation between BigInt integers and CAS integers (whatever they may be, symbols?).
Wondering because I would like to implement a robust math system eventually and am not sure yet if BigInt would be pointless if you had a CAS.
What is the major difference between implementations of BigInt vs. CAS integer?

A:

Basically, a BigInt type is a CAS that knows only integers. Any CAS will include something very similar to a BigInt. But in addition to that, it needs to understand all the other objects and operations, and how they interact.
The point of a CAS is that it implements the actual mathematical definitions instead of relying on hardware-supported types that are very fast but have implicit rounding or overflows.

