Unit 1 discusses computers and their characteristics. A computer is an electronic device that can receive data as input, process it, and provide output. It responds to specific instructions in a proper manner and can perform pre-coded instructions called a program. The five main characteristics of a computer are storage, processing, input, output, and control. Memory hierarchy is explained as the organization of different storage devices in a computer system based on speed and application needs to achieve efficient processing. Faster memory is closer to the CPU while slower memory further away to balance speed and cost.