I just bought a 4Gb Micro SD Memory Card for my Mobile Phone, what makes me wonder is, how do they do it, i mean what kind of technologie are we using today to get so much storage capacity onto a piece of silicon(?) the size of 10x20x1mm.
With my first Computer a Apple 2e, i was using large floppy Disks and with my present PC i still have my 1.44Mb Floppy Drive but what happened that we now have this new kind of storage for data, please somebody give me an easy to understand explanation.
Memory cards today are almost all built on flash memory technology - so yes, they are silicon chips for the most part. A flash memory cell is a particular arrangement of transistors that will ‘remember’ a 1 or a 0 for a very long time under ordinary circumstances, but can be ‘flashed’ to a new setting by a particular pattern of electrical voltage.
There’s nothing that really makes flash memory particularly more compact than magnetic technology like old floppy drives or modern hard drives - they can be accessed without moving parts, which helps, but mostly, the miniaturization of storage devices is just a case of practice and trying really hard - in other words, Moore’s law. 
It boggles my mind too - that a memory card that can fit on one of my fingernails probably has more transistors built into it than there are people living on planet Earth today.