Atmel AT27C256R-15PC OTP EPROM - 256K (32K X 8)

The AT27C256R is a low-power, high-performance 262,144-bit one-time programmable read-only memory (OTP EPROM) organized 32K by 8 bits. It requires only one 5V power supply in normal read mode operation. Any byte can be accessed in less than 45 ns, eliminating the need for speed reducing WAIT states on high-performance microprocessor systems.

Atmel’s scaled CMOS technology provides low-active power consumption, and fast programming. Power consumption is typically only 8 mA in Active Mode and less than 10 μA in Standby.

These are plastic 28-pin DIPS, and there is a data sheet here.