In 1986, computers were novel and big. But, it shows how forward thinking that Joe was when they included Mainframe as a computer specialist. The figure is solid. The grey body was a rarity at the time and the silver and black highlights make for a pretty solid figure. For me, Mainframe was always an older guy who had great wisdom that was of benefit to the Joe team. There's a decent amount of material on the figure/character out there. Here's the best of him from around the web.
Mainframe Video Review
Mainframe at JoeBattleLines.com
Mainframe at 3DJoes.com
Mainframe at JoeADay.com
Mainframe & Zarana by GI_JoeisThere
Mainframe by Otto the Otter
Mainframe by Flatline