Acts as the middleman between the user and the computer hardware. Allows user to run other application on a computing device. Manages the software and hardware. Focus on convenience, ease of use and good performance. Individual usability and resource allocation . Optimization for usability and battery life. Decides between conflicting requests for efficient and fair resource use . Controls execution of programs to prevent errors and improper use of the computer. Software the supports computer’s basic function. The heart operating system and “the one program running at all times on the computer” . Initializes all aspects of system. Loads operating system kernel and starts execution. One or more CPUs, device controllers connect through common bus providing access to shared memory. Copying of data from slower to faster storage temporarily. Faster storage (cache) is checked first to determine if the information is available . Allows data transfer from main memory to a device without CPU intervention. Used for high-speed I/O devices that are able to transmit information at close to memory speeds. The only large storage media that the CPU can access directly. Can store large amount of data. abbrev of ram. abbrev of rom.