This is a short segment of A-form DNA
This is a spacefilling model, colored CPK, viewed from the side.
Note the 2 grooves. The major groove is the one that is narrow but deep. The minor groove is wider but very shallow.
This shows the 2 strands colored violet and cyan. The right-handed twist can be seen.
An endview shows that the double helix is much wider than B-form DNA, and that a channel appears down the center. This is because base-pairing does not occur across the center of the helix.
An isolated view of several base pairs.