1 (filtering) A logical operation carried out on a byte, word, or field of data in order to modify or identify a part of it. A bit pattern — the same length as the item to be masked — is generated and stored in a register as a mask. By use of the appropriate operation, e.g. subtract, logical AND, logical OR, the mask can be used to suppress bits in the data, or set them to zero, etc. The process is used for purposes such as identifying the presence of high-priority bits in a status byte or resetting interrupts.
2 The use of a chemical shield, the mask, to determine the pattern of interconnects in an integrated circuit. Read-only memories (ROMs) and programmable logic arrays (PLAs) are customized for their particular applications by the masking process, unless they are field-programmable. See programmable devices.
3 A technique used in software for manipulating graphic images. An area of the image may be defined by a mark based on color, brightness, or some other parameter. The mask can then be used to allow separation of parts of the image.