Perhaps part of the things causing confusion is your mind is subconsciously thinking of styles and instruments interchangeably. If I'm wrong, please just skip the rest of this post.

A style defines the initial feel (swing or straight), time signature (3/4 or 4/4), tempo (BPM) and mixer settings of a song file. Styles can also have midi patterns embedded in the five accompaniment tracks of piano, bass, drums, guitar and strings. Band-in-a-Box and RealBand can use the midi patterns embedded in a style to create midi data for playback by midi instruments when a track is assigned a midi instrument.

PG Music uses two basic musical instrument groups, audio and midi. Audio musical instruments include: Acidized audio loops, RealTracks, PG Music Artist Performance Tracks, UserTracks, user audio files and user or third party created Artist Performance Tracks. Who knows, I may have forgot to mention one or two audio musical instruments.

Midi musical instruments include regular midi and PG Music's SuperTracks. Regular midi uses midi data generated by the midi patterns inherit in a style and an instrument patch initially selected by a style However the instrument patch can be substituted by the user. PG Music's SuperTracks use midi data and Hi-Q instrument patch embedded in the SuperTrack. Any midi data or instrument selection in a style is ignored. SuperTrack Hi-Q instruments can be substituted but using non Hi-Q patches can be difficult.

The difference between Band-in-a-Box and RealBand can be simplified as: Band-in-a-Box requires a style to open and operate. RealBand requires a style only to create midi data. Band-in-a-Box generates all tracks that are not frozen. RealBand generates what a user selects. Both programs require a chord sheet.
Jim Fogle - 2021 BiaB (822) RB (Build 3) Ultra+ PAK
Cakewalk - Zoom MRS-8 recorder
Desktop: i7 Win 10 build 2004, 12GB ram 256GB SSD, 4 TB HDD
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