The MOS Technology 6581/8580 SID (Sound Interface Device) is the built-in Programmable Sound Generator chip of Commodore’s CBM-II, Commodore 64, Commodore 128 and Commodore MAX Machine home computers. It was one of the first sound chips of its kind to be included in a home computer prior to the digital sound revolution.
You will notice that the photo of the SID chip above is not on a Commodore PCB. More info about that will be posted later this weekend 🙂
From the date code on the SID in the picture above, you can tell it was manufactured in 1992, week 25. So this would be one of the last SID chips to be made.
You can read some more about the SID chip on this wikipedia page.