Nonvolatile memory, like in flash drives has a much faster read write speed than platter storage, like in a hard drive. It also has a much smaller form factor. However, it has a much shorter service life, and data on a flash drive will degrade over time (even sitting on a shelf) in a way that platter storage will not.
If you’re looking for a way to trundle copies of data to and fro, get a flash drive. If you’re looking for semi-permanent backup or supplemental always-connected file storage, go with a hard drive.
Never, ever back anything important up solely on flash media.
Those cheapo flash drives are counterfeits that tell the PC that they have more storage capacity than is actually available, then loop around in the memory address space and overwrite existing data as you try storing more stuff on it.
As a simplified analogy, imagine a storage device that can store numbers going from 00000 to 99999, but it tells the computer that it can store numbers from 000000 to 999999. As long as you’re storing a five-digit number, it seems to work fine, but the first digit gets overwritten with the sixth if you try storing six digits at once, resulting in data loss.
The reason hard drives have stuck around despite being slow and fragile due to their mechanical parts is precisely because they’ve remained cheaper per gigabyte than flash memory.
HDDs (Hard Disk Drive) have disks, just like name implies. That disk has all data stored. To read specific info, we have to have reader over that part of disk. That one reader has to be able to read data from any place in the disk. It’s done by having stationary reader and rotating disk.
Now, if we want to read data from that disk, we have to wait until part of disk with wanted data is under reader. It may be the smallest time period ever, but it’s not zero. Multiply that by trillions of read operations and you get quite significat time passage.
SSD (Solid-State Drive) uses semiconductors to store data. Impprtant thing is that time we need to access any of that semiconductor is the same and we don’t have to wait idly.
As you noticed yourself, disks are cheaper than semiconductors, they also last longer. But the speed factor is more important for many people.
There are also other factors, like data fragmentation. If I want to read 100 bytes of data from HDD, it would be nice if these bytes are one after another. In worst case scenario, bytes are reversed: I read one byte, then I need to wait for disk to make almost full rotation to read the next byte, just because of the way it was stored. That splittinf one file into separate sections and having them in a messy way is data fragmentation. SSD don’t have that problem. I mean, they do have data messed around, but since read time is constant, it does not create any problems no matter how messy it gets.
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