Servers, Servers everywhere but not a bit to drink!
As I outlined when talking about the DAC, music data is sent serially to the DAC. I like the record player analogy. The stylus on the turntable is transferring what is in the grove at this very second.
So what does the server or streamer do? In the most basic form, it provides the user interface to operate the software. That software then reads the data from the local hard drive, or it connects to an online service and reads the music file data from there. Finally, it sends that data to the DAC for decoding and playback.
Streamer or server software can be designed to run on all kinds of hardware: your PC or Mac, or NAS, an iPhone or iPad. In more advanced systems the server/streamer is run on dedicated equipment purchased for the purpose. One example is the Chord Poly. It is a dedicated streamer that only works hooked up to a Chord Mojo DAC/AMP. There is streaming software built into some network bridges like the Sonore Rendu series. Another example is the Roon Labs nucleus products that are purpose-built for this work.
The Roon Labs How Roon Works webpage is a cleanly done pictorial overview of their software. They break their system into multiple parts and explain them succinctly.
I have a lot more to say about servers and software. There will be more posts on this subject.