I hope you did not pay too much money for this chip off ebay. It is an antiqye EPROM based part. The window is a quartz port through which you can erase the part similar to an old EPROM. Today you can buy nice electrically re-programmable FLASH parts of similar ilk but CMOS in technology that are are easily programmed with In System Programming technology....look into 89C5xxxx type parts.

Michael Karas