The so-called information processing viewpoint is to compare the human brain with a computer, and to treat the human brain as an information processing system similar to a computer. However, this analogy is only functional, that is, an analogy at the behavior level, regardless of its material composition. The difference between biological cells and electronic components. In other words, this analogy involves only software and not hardware. What does hardware mean in this passage? ['Functional properties.', 'Behavior level.', 'Material composition.', 'Biological cells and electronic components.']