The Executive and Interpreter

In the most elementary computers, executing a program is a relatively easy task. Without having to accommodate multiple programs with potentially conflicting requirements, the user only has to load the instructions into memery, set the starting address, and watch it run. Indeed, for early computers (and specialized controller chips today), this “load and go” methodology works acceptably well. For the first decade of the computer age, the modern concept of an operation system simply did not exist. Programmers were required to write software to operate tape drives, printers and other peripherals in addition to the logic required to solve the business or scientific problem at hand. Over time, primitive ‘executive’ programs were introduced to reduce the burden of managing hardware. Rather than directly commanding a device such as a card reader, a program would invoke a pre-written routine to operate the external hardware on its behalf. Delegating such ‘low level’ operations to standardized and (hopefully) reliable interfaces improved productivity tremendously by eliminating the tiresome chores of system management.