Question: I'm currently attending a basic course on real-time embedded systems. Recently, we have been talking about embedded systems memory architecture. When doing some extra studying on memory maps, I came across the memory map for the ATmega328P microcontroller. As can be seen from the image, the flash is divided into a boot section and an application section.

[![enter image description here](https://i.stack.imgur.com/NWBNO.png)](https://i.stack.imgur.com/NWBNO.png)

Why is the boot section not starting from address 0? As I've understood it, the microcontroller application won't run without a bootloader. So why doesn't the bootloader occupy the lower addresses if everything else relies on it?

Answer: 
Good comprehensive posts, so just a couple of cents in addition:

For audio reproduction, perhaps the key property of the DAC is its nonlinearity, or Integral Nonlinearity (INL).

R2R DACs don't offer advantages here, so are being successively abandoned in favor of cheaper and more flexible Delta Sigma DACs. Digital compensation for INL also favors Delta Sigma DACs as they implicitly come with beefier DSP units integrated/attached.
I can't add much to the above excellent contributions, except to add that if you have a voltage available of 30V pk-pk in the analogue domain, then 16 bit resolution equates to about 460uV pk-pk or around 160uV rms. So if your analogue circuitry is not giving less than this as noise - across the full 10 octaves of the minimal audio range (20Hz-20kHz) that is - further discussuions about the resolution of the converter are probably looking at the wrong thing.

For reference that -160uVrms is -74dBu. In my experience of making audio measurements, if you measure less than -80dBu output noise in a typical circuit, you're doing OK. -90 is very good.

And that is with +/-15V rails on the analogue side of the converter - if you are dealing with only 6V or 3V3, and 24 bits, sampling at 96kHz, of course it all gets even more difficult.

If you are making an ADC, you are likely samping a lot of low level analogue noise from input circuits.

If you are making a DAC, the output noise of your gain stages following the DAC might be more important than the DAC itself.

In reality I suspect many "high end" ADCs/DACs with 24bit resolution are actually losing at least a few bits just because of analogue domain stuff.

If you are curious about whether or not you can really hear all those bits, [the redoubtable Ethan Winer has some interesting things to say about it here](http://ethanwiner.com/BitsTest.html). You can even take part in his interactive test by downloading and listening to some files.