Traditional Japanese sliding doors and track system used to be made of just natural material, wood and paper. Shoji is changing to fit in modern lifestyles, but the basic idea of the track system remains unchanged.
Inside of a traditional Japanese house, there are very little permanent wall. Rooms are separated by corner posts that support beams. If there is a typical 6 feet wide opening, there would be two panels of 3 feet (plus a stile width) wide shoji door. One track is on the floor and the other track is at the top. The top rail is attached to the bottom side of a beam. Two grooves are cut on each rail. The top grooves are 5/8 inch deep and the bottom grooves are only 1/16 inch deep. The top and bottom of the doors are cut with a matching L-shape tenon, and they slide along the groove effortlessly.
(Figure 1) 2 panels on 2 grooves
Two panels on two grooves (Figure 1) slide and pass each other. When open, that means two panels on one side stacking over another, there is 3 feet opening at maximum. When closed, the width of the stile is overlapped in the middle, so you won't see any crack of light in between two doors, covering 6 feet altogether.Another common pattern is four panels on two grooves (Figure 2). From left, the first panel on groove A, the second panel on groove B, they can pass each other. The third panel is also on groove B, butts against the second panel. The fourth panel on groove A, so the third and fourth are mirror reverse from the first and second panels. The second panel slide to the left and the third panel to the right, making the full opening of 6 feet. When closed, the four panels take up 12 feet.
(Figure 2) 4 panels on 2 grooves
Two above are common and traditional in Japan, but there are so many variations possible. For example, instead of stacking one over another, they can open to both sides and slide along adjacent wall surfaces on a single track (Figure 3). When closed, they meet in the middle, much like the two middle panels of four-panel-system above. This can be done when there is enough space on the wall. Even if that's not the case, they can slide into a wall pocket making a shoji pocket door. These are not typical but innovative ways to implement shoji into western style homes, which is more popular among new generations in Japan.
(Figure 3) 2 panels on 1 groove