How Do Multiple File Downloads Work?

Think of it like having several phones. Each phone can connect to a different server, and servers can handle multiple connections simultaneously, similar to making multiple calls. Once a connection is established, your device can only talk to one server at a time, but it switches between established connections quickly, making it feel like you’re downloading from multiple servers at once. However, there’s a limit on how many connections you can manage due to overhead from maintaining those connections. Both your device and the server have bandwidth limits, so splitting bandwidth too thin can slow everything down too. For example, if you’re trying to load a webpage with multiple resources like text, images, and videos all at once, it might be better to load them in parts rather than all together, to avoid waiting too long for anything to finish.

Files are made up of packets and streams in the digital world. The main protocols here are TCP and UDP. TCP is connection-based (like a phone call) and guarantees the order of data, while UDP is faster but delivery isn’t guaranteed. When you download files, your browser typically makes multiple HTTP requests to get the various components of a webpage at once, often making multiple connections to retrieve these items, even if they are technically 'files.' If you're curious, you can open your browser's developer tools and watch all the network connections happening in real-time when a page loads!

On the technical side, a TCP/IP connection is identified by a combination of source and destination IPs and source and destination ports. Since you can have around 64,000 simultaneous connections (limited by the number of available source ports), theoretically, you could download many files in parallel. However, the physical hardware won't always support using that many connections at once due to practical limitations.

This is a bit more technical, but a PC or server can maintain hundreds of connections at once without you realizing it. If you're on Windows, your OS constantly checks for updates and may download necessary files from other computers on your network. Things like your CPU, RAM, bandwidth, and hard drive speed can all limit your download speeds. Sometimes, a server might be able to send data faster than your hard drive can write it! Also, when downloading from multiple servers, you can pull pieces of a file from different locations, which is a common practice with torrenting.