The M27C400 is an 4 Mbit EPROM offered in the two ranges UV (ultra violet erase) and OTP (one time programmable). It is ideally suited for microprocessor systems requiring large data or program storage. It is organised as either 512 Kwords of 8 bit or 256 Kwords of 16 bit. The pin-out is compatible with the most common 8 Mbit Mask ROM. The FDIP40W (window ceramic frit-seal package) has a transparent lid which allows the user to expose the chip to ultraviolet light to erase the bit pattern. A new pattern can then be written rapidly to the device by following the programming procedure. For applications where the content is programmed only one time and erasure is not required, the M27C400 is offered in PDIP40 package.