I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Many machine models different from the standard multi-tape Turing machines have been proposed in the literature, for example random access machines. Perhaps surprisingly, each of these models can be converted to another without providing any extra computational power. The time and memory consumption of these alternate models may vary. What all these models have in common is that the machines operate deterministically."? 

How many types of machines have been suggested?