In 1957, IBM began the construction of the Semi-Automatic Ground Environment, by far the world’s largest computer. Spanning more than 20 different locations, each equipped with acre-sized computers and connected by a nation-wide network of bleeding-edge 1,300-baud modems, SAGE was the pinnacle of the United States’ Cold War radar and missile air defenses.

SAGE, like most supercomputers, was built to solve a big data problem. During the Cold War, hundreds of radar installations across North America were constantly on the lookout for Soviet missiles and bombers. As you can imagine, these stations produced a lot of data — a lot of data that needed to be analyzed and acted upon immediately. With the physical size of the US, the high speed of modern jet aircraft, and the sheer number of possible attack vectors, the US military decided that a network of computers was the only viable solution.

SAGE consisted of 20 or so Direction Centers, each of which was a windowless, one-acre-large concrete cube (see below). Inside each DC were two CPUs, each one measuring 7,500 sq ft and consisting of 60,000 vacuum tubes, 175,000 diodes, 13,000 newfangled transistors, and 256KB of magnetic core RAM, consuming a total of 3MW of power and weighing in at 250 tons. Each CPU — only one operated at a time; the other was kept as a hot spare to minimize downtime — was capable of executing 75,000 instructions per second, which was enough to spit out tons of radar data to 150 CRT consoles.

According to Scott Locklin, this was the first system that used CRT (cathode ray tube) monitors, and the first to use magnetic core RAM. (See: The history of computer storage.) As you can see in the photo below, SAGE operators used light pens to interact with their CRTs — another first, some 30 years before the arrival of the NES’s light gun Zapper.

Each of the Direction Centers was connected to each other, a handful of Command Centers, and hundreds of radar centers, by AT&T telephone lines (running through a central, hardened underground bunker) and microwave towers. At the end of each telephone line was a Bell 101 modem — the first mass-produced modem, and the first device to use ASCII. SAGE was one of the first wide-area networks, and many of those who worked on SAGE would go on to be involved with the creation of ARPANET in 1969. ARPANET, if you weren’t aware, is what eventually became the internet.

At this point you might be wondering what the “semi-automatic” part of SAGE is. Believe it or not, SAGE was actually equipped with the technology to launch and control interceptor planes (such as the F-101B Voodoo and F-4 Phantom), and air defense missiles. Scarily enough, one of the missiles that SAGE could launch and control was the CIM-10 Bomarc (video below), which was equipped with a nuclear warhead. SAGE communicated with aircraft and missiles via HF, VHF, and UHF radio signals transmitted from the radar stations.

All told, the SAGE system is estimated to have cost around $10 billion dollars in 1954, or about $67 billion in today’s money — or about three times what the US spent on the Manhattan Project during World War II. SAGE remained in continuous operation between 1963 and 1984, with thousands of people all over North America constantly scanning their radar screens for Soviet attacks, all hankering for an opportunity to launch a radio-controlled nuke. As we now know, though, SAGE probably saw little if any action throughout its 21 years of operation. Before you label the $67 billion price tag as exorbitant, though, remember this: If SAGE had never been built, we might be living in a world without the internet, without IBM, without air traffic control systems, and perhaps we’d all be calling each other comrade.

For more information about SAGE, watch the 20-minute infomercial — produced by the US Air Force itself — embedded below.

Now read: The history of supercomputers

[Image credit: Jurvetson]