A computer is an electronic device that can read, write, compute, compare, store, and process large volumes of data with high speed, reliability, and accuracy. There are three main types of computers: analog computers which operate on continuous ranges of values or voltages, digital computers which operate using binary numbers of 0s and 1s, and hybrid computers which combine aspects of analog and digital computers. Key features of computers include high speed, reliability, accuracy, large storage capacity, and versatility.