Welcome to the Forum.
Days before RealDrums & RealTracks
1. Band in a Box = an auto accompaniment program that had 5 "tracks" of backing musicians. One track for a soloist ,one track for the melody. These 7 tracks were all MIDI tracks. There was also one track for the user to record audio of his own,eg Guitar,vocals etc.
2.STYLE is made up of the 5-7 instruments mentioned above that will play your chord progression based on the STYLE chosen. There are 1000s of STYLES to choose from with subtle variations.
So in it's simplest form you type in chords,choose a STYLE & hit play. Want some real fun type in the chords to a familiar song and go through the STYLES choosing stuff that's way off base.

OK now moving on to NOW. We have all of the features as mentioned above and everything works just the same.The big difference is the introduction a couple years ago of RealDrums & RealTracks. What PG did was to get REAL Musicians into the studio and have them record varying instruments playing all sorts of parts. If you are familiar with Looping" like in programs like Acid you get the concept. The big difference between ACID & BIAB is that BIAB picks the parts for you and arranges them.It's the same with RealDrums.So now in BIAB you can have all MIDI players, all Real players or a combination of the two.
REAL STYLE = a style as mentioned in the old days but it may utilize one or more of the RealTracks players & RealDrums.The cool thing though that is different from the old is that you can type in your chords and NOT choose a STYLE. You can RT Click on each of the 7 instruments at the top and pick "add/remove RealTracks" This releases you from the confines of pre-made STYLES. YOU get to choose the players. Unfortunatly we are not yet able to do this mix and match with MIDI players.

OK RealBand is a full blown sequencer that has most of the features of BIAB but has slots for 48 tracks as opposed to 7.And BIAB only has 1 audio track to record to. RB has all 48. Most of us rough out the song in BIAB then import it to RB and continue on to completion. I have a friend that is a pro jazz guitarist and he only wants:
1.Bass
2.Piano
3.Drums
in his Band so he just uses BIAB. No real need for RB.
Hope this helps some.

John
ESI Gigaport HD+
Lenovo Turion II /4 Gig Ram/ Win7x64 be
15.6" Monitor
"The only Band is a Real Band"
www.wintertexaninfo.com/BANDS/JohnnyD.php