All your replies are helpful. I am just starting using the Atmel platform, and it's not all obvious to me.
So the USB/serial converters can program the 328 for instance, using the bootloader?
Is it wrong the Arduino also is capable to write the bootloader on a blank chip?
What I don't fully understand there also only seems to be some kind of USB/serial converter IC.
I am more interested to flash chips directly, not using a bootloader.
Or what is the advantage of having a bootloader? I have been thinking about that but did not figure out why people use a bootloader.