I need the name of a cord please?

I have a macintosh classic and a tower thats not apple made. Ive looked everywhere for a the cable that connects them together for the display. All I can find are little blue ones. But I need a bigger one, that's kinda purple( if that makes sense). I thought they were called VGA but when I search that I get the little blue ones. Is there a name for the one I need?