The security and reliability offered by legacy computer systems seem to be among the reasons why a 16-bit IBM minicomputer first sold in 1976 is still being used by the U.S. Air Force to "coordinate the operational functions of the United States' nuclear forces, such as intercontinental ballistic missiles, nuclear bombers, and tanker support aircrafts."

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A 16-bit IBM Series-1 minicomputer using 8-bit character encoding might play a key role in launching the United States' Minuteman-III nuclear-armed intercontinental ballistic missiles (ICBMs) against either China or Russia should it come to this. This model is one of the great grandfathers of today's 64-bit desktop PCs.

The Air Force operates some 450 Minuteman-III missiles in blast-proof silos located at secure air bases in Montana, North Dakota and Wyoming. A Minuteman-III can deliver its 300 kiloton W-87 thermonuclear warhead to a target 13,000 kilometers away.

The distance from Wyoming to Moscow is some 8,500 km. The distance to Beijing is 9,700 km.

But there seems to be a method behind this madness of using a 16-bit computer that stores data on 8-inch floppy disks. One source claims legacy systems being low-tech is safer and probably more "hack proof" that current digital systems. There's also the reliability issue.

This Series-1 seems to have been doing a great job for close to half a century so why fix something that isn't broken?

"This system remains in use because, in short, it still works," said Pentagon spokeswoman Lt. Col. Valerie Henderson.

And change always comes hard to the military. But the U.S. Government Accountability Office is bent on forcing the Air Force to ditch this legacy IBM in favor of newer machines.

The Pentagon has announced its replacing the 8-inch floppy drives on the Series-1 with Secure Digital devices by the end of 2017. It plans to fully replace the IBM system by the end of 2020.

TagsIBM Series-1 minicomputer, intercontinental ballistic missiles, U.S. Air Force, 8-inch floppy disks