1950 to 1959: Starting the Ascent of Digital Computers and Software - The Technical and Social History of Software Engineering - page 82

The SAGE air-defense system would soon create the world's largest digital
computer and the world's largest military software application. The convergence
of computing, software, and defense was about to hit full stride.
The SAGE project was a landmark in several respects. Perhaps the most im-
portant is that it marked the transition of digital computers from dealing with a
narrow band of specialized problems to tackling huge and diverse problems of
enormous complexity. It is not even remotely possible to provide an effective air-
defense system for an entire country without the use of fast digital computers to
aggregate all of the torrents of incoming data from thousands of sources.
SAGE also marked a transition between batch computation, which could take
place at a time convenient to the engineers, to real-time computation, which pro-
cessed new data instantly as it occurred. In future decades, real-time computation
would lead to new forms of embedded computers that were located inside of phys-
ical devices such as automobiles and would constantly monitor and control things
like brake systems and fuel injection.
Another important transition introduced by SAGE was continuous operation
with high reliability 24 hours per day, 365 days of the year. Prior to SAGE, com-
puters would work for a few hours and then be shut down until needed again. With
SAGE, the computers were always needed.
The need for continuous around-the-clock operation also spurred a need for
much better quality control on all software applications. That led to new features
that allowed computers to monitor their own statuses, or the status of attached
computers, and alert console operators to potential problems before they occurred.
It also introduced the concept of redundancy, or backup, computers that could take
over if a computer needed to be repaired or modified.
As a result of SAGE, within a few decades, the Department of Defense would
own more computers than any other organization in the world. Every defense de-
partment in every major country would begin to use computers as critical compon-
ents of weapons systems; air defense; and all military operations on land, on sea,
and in the air.
SAGE was not just a computer and software. It was a very large and complex
hybrid system that used hundreds of radar receivers feeding real-time data into 24
Direction Centers, each of which was a large building housing at least one IBM
AN/FSQ-7 Combat Direction Central computer.
The SAGE system interconnected all the Direction Centers, and it also connec-
ted with the Army air-defense command posts. Many missile launch sites were