Retrotronik RAM card for HP 48GX

[Eric Rechlin]

If you try to use a 4 MB card, the last port won't show up and you will get a perpetual Invalid Card Data error message on powerup. There was a resolution to this with a special switch on some cards to allow you to switch two of the top banks and properly initialize all of them to avoid the error.

I don't recall them ever being available in mass-produced form (only in the homemade-style with bare circuit boards) so I doubt many exist. I think Oliver Klotz was the only person to actually try to sell them in the latter form; apparently they cost 499 DM twenty years ago.