Eli5: Why does downloading files take so long, but copying and pasting them on the same device takes seconds?
In: Technology
Three reasons
If you’re copying it into a different file on the same hard drive, the data doesn’t actually move. There’s a registry in the hard drive of addresses of the data. When you “move” the data you’re really just updating the virtual address that directs to the physical location of the data. Since the data isn’t moving, updating the address is very quick.
If you’re copying the data to a different hard drive on the same device, you’re using connections that are usually very fast. SATA 3 is running at up to 600 megabits/second, and that connection is prioritized in your device. Not much else will be using that connection at that time, so it gets most of that 600mb/s.
When you’re downloading the data from online you have to copy all of the data from their hard drive somewhere to your own hard drive. That connection has several bottlenecks. It can’t be any faster than your download speed, which is maybe 100mb/s unless you have fiber or whatever. Their upload speed is probably similarly limited, probably less than your full download speed. Moreover, it’s likely that many people are trying to download that data, so their upload speed is being split between all of the users – in actuality, their overall upload speed is probably loads faster than your download speed, but you’re only getting a fraction of it.
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