(DIP) vintage IC manufactured by Plessey. The part number, "8258590," "M344 B"

​Part Number & Identification

​The markings on the ceramic package are:

​PLESSEY: The manufacturer.

​8258590: The part number. This number is unique to the specific IC and indicates its function, although without further documentation, its exact purpose is difficult to determine. It could be a custom IC for a specific military or telecommunications application, which were common areas of focus for Plessey.

​M344 B: This is likely a date code, with the "M" possibly indicating the manufacturing location, and "344" representing the 344th day of a specific year. The "B" could be a revision or batch number. This type of date coding was common in the semiconductor industry.