Very likely it is a OTP Eprom, which is combined along with some DRAM, probably 256M or such, into a SIMM package so that you can simply plug in the module to do firmware upgrades. Uses a cheap commonly available SIMM socket on the mainboard ( and I guess the processor there is a 68000 series CPU as well) and footprint that is also an industry standard pinout with only a few extra control lines, normally used for communicating to the on SIMM identity, that provide the chip select and output enable for the EPROM.
Common on embedded boards, as it allows the manufacturer to provide a very easy to install upgrade, but this is still not easy to copy without some work, and is not as easy to pirate as a software firmware upgrade. I have some Tektronix Phasor printer boards with a few of these on them, providing on the one the main printer firmware and RAM, and a few more providing additional font ROM packages, complete with Adobe provided licenses as well printed on the label.