To simply affirm what the previous posters have said, C-Map cards vary with the era they were made and the equipment they are intended for. Our 1998 Echotech green-screen GPS plotter uses C-Map cards like the longer ones in your photo. Our newer Furuno NavNet VX2 C-Map radar/plotter uses C-Map SD cards like the smaller one in the middle of your photo.
Also, the SD card in your photo is a C-Map Max card. This is not the same data format as the older C-MapNT. The Max cards, as the name implies, show a much wider area with a single card as the NT cards. For example it takes eight C-MapNT cards to cover the area from the San Juan Islands to the north end of Vancouver Island and Cape Caution across from it on the mainland.
It takes just two C-Map Max SD cards to cover the area from the south end of Puget Sound all the way north to Yakutat, Alaska.
I believe, but I could be wrong. that the other card in your photo, the one with the metal clip, was the card type that preceded the rectangular NT cards in your photo. Either that or it is perhaps a card that was made for a very specific plotter. It's not an SD card.
But I think that in the late 90s/early 2000s, all or almost all the C-MapNT cards did indeed look like the longer ones in your photo and the plotter manufacturers all used the appropriate reader. For example not long after we got our big Echotec plotter we got a Magellen handheld GPS plotter that was also C-Map. Even though it was quite small, it used the same C-MapNT cards the Echotec did.
When the smaller but more data-capable SD cards became popular, the C-Map folks changed over to them and the manufacturers installed an SD card reader in their plotters. A few years ago we bought a Standard Horizon C-Map GPS plotter for one of our other boats and it, too, uses SD cards.
As others noted, the two kind of cards are not interchangeable in the readers.
