Here's the short: It was an add-on system for the Famicom (what the NES was in Japan). We have to assume that the little pic you have there is an A/V Famicom and not a top loader NES.
The FDS used magnetic disk similar to floppy disks. A lot of popular NES titles originated on the FDS, some had differences. Differences include graphics, sound, music, and the ability to save. For example, Metroid lets you save in the FDS version while the NES version has a password system. The FDS allows for extra sound channels, so some games have different sounds.
I went back and forth for years thinking about getting one. And now that I own a Famicom, the temptation was even greater. Problem is reliability. I wouldn't want to spend the money on one ($50-150) only to have problems using it. The disk can get dirty and wear out. The system has it's own problems with getting dirty and breaking down.
Fortunately, the PowerPak NES flash cart now lets you run FDS ROMs from it. I played Doki Doki Panic, Metroid, and Castlevania (all FDS versions) using the PowerPak and was very impressed.
Yeah, unlike the toaster NES and original Famicom, the top-loader NES and A/V Famicom look pretty identical. The big differences is the NES has a 72-pin cart connector and the Famicom is 60-pin. And the A/V Famicom has composite A/V out (while the original FC only had RF) and the top-loader NES only has RF (while the toaster had RF and composite A/V).
i got the playstation at goodwill (i actually found two in the course of a few days, i wanna paint one) w/ no controllers , but i used to rock one back in the day (n still rock some ps1 games) so it's gravy. i scored the controllers at pawn shops on the cheap... the nes ones were just a random find and i got the snes one w/ intentions of getting an adapter and using it w/ my gameboy player (oh yeah, n i got the adapter to use the nes controllers w/ my wii on the vc). i don't use a duke controller but there's no cute little icons of the s-controller. am i still cool?