I think COL Geek has nailed it. Searching for the number on the large chip., "D27C010J - 200" led me to a website
https://www.cpu-galaxy.at/CPU/Ram Rom Eprom/other_intel_eproms/other_intel_erpom.htm
that says a VERY similar number is for an Intel CHMOS EPROM, and led to this Data sheet
https://www.cpu-galaxy.at/CPU/Ram Rom Eprom/other_intel_eproms/other_intel_erpom-Dateien/D27C010_Datasheet.pdf
CHMOS, I found, is the acronym Intel used for High-Density CMOS chips.
According to this data sheet, this is a UV-Erasable EPROM, which explains the window on the top. That is, it can only be erased by exposing the chip inside to UV light. Then it can be programmed using specific higher voltages, and read at standard 5 VDC TTL voltages. Since this unit can be erased with UV light through the window, it was intended for use at the development stage of a system, where successive versions of the software could be loaded into the unit. Once the software was completely perfected, a similar version of the chip with NO window in the plastic case was available, pre-erased, to be programmed electrically and then installed in a system that would not be updated later.