Response Time - the latency between a request for service (typically by an ISR) and the generation of a response output.
Ring Buffer - a data structure which provides multiple serially reusable buffers - most often used to buffer incoming data from a device interface before it can be processed - likewise for output data before it can be transmitted.
RISC - Reduced Instruction Set Computer.
RM- Rate Montonic, the basic theory formulated by Liu and Layland for fixed priority multiplexing of a single CPU that is intended to provide multiple services over time.
RMA - Rate Monotonic Analysis,the process of analyzing the C, T, and D characteristics of a set of services to be executed on a CPU and determination of priorities according to RM policy and feasibility according to a sufficient or better yet, necessary and sufficient test.