Desktop computer. X-ray of a desktop computer from above. The computer's hard drive (permanent storage, lower left), CD-ROM drive (compact disc - read only memory, centre left) and transformer (lower right) are seen. The printed circuit board, which houses the CPU (central processing unit), RAM chips (random access memory) and other components (grey), is at centre. Various external ports (far right) are also seen, which allow peripherals such as a monitor, keyboard, mouse and printers to be connected.