It’s not about getting data as dense as possible. It’s about cost. Hard drives are much cheaper than solid state storage per unit of storage. The best deals are around $15 per TB while a 1 TB microsd card is several hundred dollars.
You can get those massive densities with a hard drive like physical size. There are solid state drives that are tens of terabytes but they cost thousands to tens of thousands of dollars each.
Lol this isn’t engineering wtf.
Solid state data storage like an SD card and magnetic storage like a hard drive are fundamentally different technology; this is like asking why a VHS Tape needs to be bigger than a Blu-Ray despite the latter having a larger capacity.
The reason they both exist is that they have different characteristics and use cases. An SD card is slow but physically compact, a HDD faster than an SD but far larger and probably cheaper. An SSD is faster than both, smaller than a HDD but bigger than an SD and more expensive than both.
SD cards have only one package of memory limiting performance. Normal size (SSD) drives have multiple packages that give you much better performance: e.g. the SD card will take 8s to weite something, the SSD will only take 1s because it was able to split the write into 8 smaller pieces onto 8 different packages.
Compared to HDDs: SD cards and SSDs have limited number of writes before it dies, HDDs can be written indefinitely because it has magnetic platters that don’t degrade with every write. SD cards and SSDs also have a limited number of reads before the data gets corrupted (known as read disturb), this is more pronounced as the SD card and SSD ages. On SD cards the data needs to be manually refreshed; most SSDs will do this for you automatically; HDDs don’t have this problem.
I have actually read various Amazon reviews on 1TB SD Cards and most people claim that they either don’t work correctly, have major issues (like data suddenly being deleted), have far less space than advertised,…..etc.
Basically the number of technical issues reported with them in the reviews seemed so high that I am doubtful most of them even work correctly at all. Perhaps some very high end and high quality ones might, but otherwise I have my doubts. I would thus most likely never buy one.
The magnetic disc drives are bigger because the physical space to store the data needs to be bigger. That said – a lot could probably be smaller but we have standardized the size of a HDD so they fix into a standard drive slot in a computer.
Similarly a SSD is very often mostly empty. If you have an old obsolete one crack it open and take a look – it might be barely more than what looks like an SD drive with a little printed circuit board (PCB) that takes up maybe 10% of the case. Or google “inside SSD case”. The reason for this is the same as above – manufacturers have agreed on a standard size for a SSD case – the case gives manufacturers enough space to make the drives they need to make (some have much more complex PCBs and other supporting infrastructure inside) while ensuring all SSDs are compatible with the standard mounting station in a PC case.
Which brings us back to the SD drive, these can be just the memory chip because all the supporting hardware is inside your camera/computer so it doesn’t need an additional case. The drive is often literally the same size as the actual drive in a SSD (although some SSD drives might have multiple “SD” chips in them to get better storage (ie it might have two 240GB chips) where the SD drive is obviously only one.
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