A vector type is a simple derived type that represents a vector of elements. Vector types are used when multiple primitive data are operated in parallel using a single instruction (SIMD). A vector type requires a size (number of - elements) and an underlying primitive data type. Vectors must have a power - of two length (1, 2, 4, 8, 16 ...). Vector types are considered + elements) and an underlying primitive data type. Vector types are considered first class.