The modern structure of the Piano has six major parts viz., the frame, the sound board the strings, the action, the keyboard and the Pedal.
The Pianos are categorized as Vertical or Upright Pianos and Grand or Horizontal Pianos. Upright Piano includes the cottage Piano of late 19th century. The mode in Spinet and console are small upright cottage Pianos. The strings run in the upright Pianos vertically or diagonally from top to bottom, upright and small grand Pianos are sometimes over strung, stretching the bass strings diagonally across the shorter treble strings. The extra length gained in this process will result in improved tone quality. The combined strength of all the strings is about 14tons in an upright Piano, 30tons in a concert grand Piano and 18 to 20tons in a modern Piano on the back of the Piano not only heavier hammer and strident action but also strong structure are the requirements of these high tension springs. The tension was less in the earlier Pianos fortes.
While buying Pianos, you have to select a good model. There will be differences between various types of the same brand. Even reputed and old manufacturers use less expensive designs compromising with expenditure critical structural components. If you are not satisfied with these crucial parts, you should not take risk as they will require expensive repaints and replacements comparing the structural components in an important factor, and you have to choose a model which will be dependable and long lasting.