Single-purpose computers

Single-purpose computers were the earliest form of computing device. Given some inputs they could calculate the result of the single function that was implemented by their mechanism. General-Purpose computers have almost completely replaced single-purpose computers and in doing so have created a completely new field of human endeavor - Software Development. General-purpose computers must be programmed with a set of instructions specific to the task they are required to perform and these instructions are collectively know as computer software. The design of single-purpose computing devices and many special-purpose computing devices is now a conceptual exercise that consists solely of designing software.