The earliest example of equine footwear we have is made of animal hide and dates from about 600 B.C. This primitive hoof protector looks more like a horse bootie than what we think of today as a horseshoe. It was probably stuffed with dried grass or other available natural material and tied on with hide thongs.
The spiral model is a software development process combining elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. The spiral model was defined by Barry Boehm in his article A Spiral Model of Software Development and Enhancement from 1985. This model was not the first model to discuss iterative development, but it was the first model to explain why the iteration matters.
The idea of this approach to scanning can be traced to three sources. In 1989, the first report of a practical spiral CT scanner was presented at the RSNA meeting in Chicago by Dr. Willi Kalender5. The spiral/helical CT scanners developed after 1989 were referred to a singleslice spiral/helical or volume CT scanners.