It depends on where you're taking the reader. If you're emphasizing ontological dependence and the process is built on the computational primitives, 'because' or 'since', but if the context is to argue something and you want to show that the primitives are present, perhaps because you are drawing parallels between humans and CPUs, then 'therefore' can be used as a transition word rather than a logical or metaphysical relation. 'Therefore' has at least two functions in English, so context matters.
It's easy to forget that words have more than one use. Sometimes two subtle ideas can be expressed with the same word. In philosophy, particularly metaphysical discourse, those nuances in meanings can have a substantial impact on the ideas expressed. 'Because' and 'therefore' are two words that have the potential to have multiple meanings, and their usage to some degree requires both clarification and context. Therefore is a good example since it can be used to make claims about material implication (which is a logical relation), the necessity of existence (which an ontological relation (SEP)), or just used as a linguistic transition in the passage to organize claims.
Also, technically, it's not decided in mathematical philosophy whether procedures, which have a goal, are constructed, that is assembled from more primitive procedures, or if a procedure is somehow discovered as an objective assembly from other procedures in the way that trees are made of cells. Some mathematicians reject the objectivity of mathematics entirely. For an example of the tendentious nature of the presumptions built into mathematical philosophy, consider constructivism:
Constructivism is often identified with intuitionism, although intuitionism is only one constructivist program. Intuitionism maintains that the foundations of mathematics lie in the individual mathematician's intuition, thereby making mathematics into an intrinsically subjective activity.2 Other forms of constructivism are not based on this viewpoint of intuition, and are compatible with an objective viewpoint on mathematics.
Whether one is a realist or an instrumentalist has a lot of bearing in matters of ontological dependence.
Generally, 'because' and 'therefore' are understood as moving in the opposite direction or order, such as 'A therefore B' is similar to 'B because A'. In a formal system, logical operations can be defined explicitly as inverses, but in natural language, definitions of necessity and sufficiency, and in causality, things aren't so pat.
So, the question is what are you trying to express? If you are saying that it is necessary that long division exists because of specific processes, this is an ontological claim. You seem to be claiming that it is necessary to use a standard algorithm for division to occur inside of a computer. In fact, that's not a true claim, since the ALU of a computer neither uses base-10 nor uses the same algorithms we do to conduct math. In the instance that a number is divided by two, for instance, in a processor, it is done both in binary and using shifting. Therefore, one has to exercise caution when making ontological claims about certain general operations entailing the use of more primitive ones. Computer algorithms are a complex subject, and what you think a computer is doing and what it is really doing relies on a sophisticated understanding of mathematics, code, microcode, and logical gates so let the claimant beware.
The use of logical 'therefores' and 'becauses' are going to be determined by your the intention of your argument. An argument is generally two premises, one explicit at least, that arrive at a conclusion. Here in your example, you only provide one claim, so it's impossible without context to decide. Are you presenting a formal or informal argument about computers and division? We simply can't tell. Lastly, 'therefore' can be used as a transition word. Are you attempting to guide the user through the passage? Again, without a passage, we cannot tell.
Ultimately, the right use of word is going to depend on your intention and the context the sentence you provide is invoked in.