XSp.

Here’s a DOS game that’s probably the first fixed screen shooter I’ve ever played:

Operation Wolf was originally a sucessful Taito arcade game that ended up ported to tons of other platforms.

I remember playing it on a PC-XT, the game used two 5 1/4 floppy disks…. 640Kb each if I’m not mistaken.
And I played it both in a monochrome green screen and in an ancient 4 color display.

Original Arcade version:

Funny story back then… for some reason (most likely a virus), the game would sometimes run, sometimes not, sometimes it would lock up, mainly while changing floppies.

ZX Spectrum version:

But I liked the game a lot, so I’d keep trying… and I didn’t know much of how those floppies worked…
I thought it was some kind of contact problem so I kept wiggling the floppy inside the drive hoping this would help the game to run… 😛

NES version:

Luckly I didn’t damage those floppy drives, but I also couldn’t play much of the game because of those problems… I still remember some funny things about it though, like having to shoot pigs to get ammo. xD