The 28 pin Window Ceramic Frit-Seal Dual-in-Line package has transparent lid which allows the user to expose the chip to ultraviolet light to erase the bit pattern. Anew pattern can then be written to the device by following the programming procedure. For applications where the content is programmed only on time and erasure is not required, the M27C64A is offered in Plastic Leaded Chip Carrier package.