Uhmm- this is mostly speculation and reverse engineering, and a specialist in digital camera design ( electronics engineer and/or software expert) could give a far more useful answer -
In a shot you take with a digital camera, well, you have light falling on a photosensitive bit inside the thing, which is divided into a whole lot of segments. Each segment is polled in some sort of order - left-right and top-bottom maybe, and a value for what it saw is recorded and probably pre-processed to some extent, perhaps to make it into a particular file format like a JPG. Then it’s sent to the storage area of the camera.
Now, a video camera can do it a whole lot faster, not least because the image it is shooting is typically only 640x480 ( pixels…dots of color, ya know?) while most any self-respecting recently made digital camera will be doing something around 4 times the width and 4 times the height to make a file 16 times the size. At least.
This is where it gets entertaining… no matter how big a storage chip or card or stick you have stuck on the thing, the speed at which the camera will do another shot ( or finish the first one) will likely depend on how fast the internal processor is in the camera, how much internal memory it has and how fast that is and just how cleverly the internal software in the camera itself was written.
It’s not a matter of how fast it gets sent to the storage chip or card, that’s silicon chip-silicon chip and effectively instantaneous over such a short distance, it’s how fast it was made ready to send.
An analogy - you can have a gigantic hard drive in your computer, but if it doesn’t have a particularly fast processor or much RAM, and if the software you’re running isn’t that small, it’s gonna be slow. Add RAM, a faster processor and maybe clean up the software and it’ll go faster.
Similarly, if I am, say, running an older version of a spreadsheet on an older computer with less speed and memory, it gets done pretty much as fast as it would on my fastest machine with the newest version 'cos the new versions of that spreadsheet are downright huge. Millions of lines of code versus tens of thousands of lines of code.
And this is where the high-end digital camera stuff tends to justify its existence. More expensive camera, they can afford to throw in more and better processors, more internal memory and pay their software people to grind down the code some to be as fast-running as possible.
I do know that my pro photographer friends’ gear will do sequences ( and get a shot taken) faster, with less shutter lag than I can with my relatively inexpensive Fuji. Which can be explained, really, only as I have above.
And it’s also why software and firmware updates for digital cameras are something to pay attention to…they can change the performance of said camera quite a lot.
hope that’s of use
doc…