While there is great variety in the construction details of bows (both historic and modern), all bows consist of a string attached to elastic limbs that store mechanical energy imparted by the user drawing the string. Bows may be broadly split into two categories: those drawn by pulling the string directly and those that use a mechanism to pull the string.
Directly drawn bows may be further divided based upon differences in the method of limb construction, notable examples being self bows, laminated bows and composite bows. Bows can also be classified by the bow shape of the limbs when unstrung; in contrast to simple straight bows, a recurve bow has tips that curve away from the archer when the bow is unstrung. The cross-section of the limb also varies; the classic longbow is a tall bow with narrow limbs that are D-shaped in cross section, and the flatbow has flat wide limbs that are approximately rectangular in cross-section.
The classic D-shape comes from the use of the wood of the yew tree. The sap-wood is best suited to the tension on the back of the bow, and the heart-wood to the compression on the belly. Hence, a cross-section of a yew longbow shows the narrow, light-coloured sap-wood on the 'straight' part of the D, and the red/orange heartwood forms the curved part of the D, to balance the mechanical tension/compression stress. Cable-backed bows use cords as the back of the bow; the draw weight of the bow can be adjusted by changing the tension of the cable.
They were widespread among Inuit who lacked easy access to good bow wood. One variety of cable-backed bow is the Penobscot bow or Wabenaki bow, invented by Frank Loring (Chief Big Thunder) about 1900. It consists of a small bow attached by cables on the back of a larger main bow.