Welcome to the SDMB, CuriousGeorge!
If the human brain/computer analogy works at all, I think it’s only in respect to memory. Even then, it’s still pretty weak. Memory is theorized to work on a basic encoding-storage-retrieval model, just as computers do, but as sethdallob said, computers don’t think. They don’t attach any emotion to the information they store in memory as we humans do with our memories of events and experiences.
However, I have read that the human brain can store the equivalent of about 500,000 text pages’ worth of information. Don’t have a cite for that one, though. My text here says that one scientist estimated that the human brain can hold one billion bits of information in memory (presumably long term memory). When it comes to short term memory, on average, a person can retain a list of seven items: for example, seven items of a grocery list, or seven digits (which comes in handy for remembering telephone numbers).
Not sure about your OS question. If humans do run on an OS, then we all got the same one, and there ain’t gonna be any upgrades anytime soon, so far as I can tell. Multitasking? You know, some people can’t even dress themselves if they wake up too early in the morning…