RAM allows data to be read and written in roughly the same amount of time regardless of the order accessed, unlike storage media like hard disks that are slower to access data in some locations. A CPU carries out computer program instructions by performing basic arithmetic, logical and input/output operations. A GPU is specialized for rapidly manipulating memory to generate graphics and is more efficient than CPUs for parallel processing of large data blocks. Common display technologies include LCD, CRT and plasma which present video output across a full rectangular area.