It&#x27;s modular arithmetic because of the internals of the processor, not because of some law-of-the-universe.<p>It could just as easy a processor not allow over- or under- flow operations. However, it&#x27;s easiest to just truncate the number and essentially do modular arithmetic. That&#x27;s the difference. Over- or under- flow, checked, wrap-around all refer to the state at which the operation&#x27;s answer needs more space than it is given. Modular arithmetic and checked instructions are what to do in those situations.<p>Aside, division in modular arithmetic can be done, but it&#x27;s not what most people want (hence why usually not performed). 4 &#x2F; 3 mod 7 -&gt; 4 * 5 mod 7 ( 5 is the multiplicative inverse of 3 mod 7 ( 3 * 5 = 1 mod 7) -&gt; 6 mod 7