Perhaps if we take a step beyond the lingo and talk about it more in terms of what it actually does depending on what the radio station is feeding it.
If you are getting a signal from a station that only supports the most basic type of service, you will get the scrolling line all by itself. In the picture above, that is the line that has "....Hits today. Classics....", in it. As far as your ipod is concerned, this is just text. It cannot do anything with it but display it. There is nothing in that data to tell the nano what information is in that text. Call it what you like, but that is what it is. If all you get when you are tuned to a station is that line, you will not get anything saved into your "recent songs" list. Some stations won't even give you that line of text.
However, stations that transmit with truly "tagged" data - in other words, there is a signal that identifies the text by labeling some if it as "Artist" and some of it as "Title" - then you will see the actual song name, "Like a Rolling Stone" in the example above and artist, "Bob Dylan" in the example above. When the nano gets this data, formatted in this way and with the tags, you will get things showing up in your "Recent Songs" screen. You will also see the icon in the lower left that lets you tag it as a favorite song. However, the bottom line here is that if you do not see the name of the song and the artist as shown in the example above, then the nano is NOT getting enough info to figure out what the artist and song are.
Many people make the mistake of thinking that if they are getting the "....Hits today. Classics....", that the ipod should be able to know what song is playing because stations will often have the name of the song in that scrolling text. However, this is NOT the case. If you don't get the artist and title above the scrolling text, then your iPod has NO IDEA what the name and artist of the current song is - no matter what it says in the scrolling text. The only way the nano can show you recent or favorite song is if it got that artist and title information.
Finally, if there is no icon in the lower left of the screen as show above, you also know that the ipod is not getting enough information to know the artist name and song title If it was, it would show you that icon.
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