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The Sentry 400 was Fairchild’s response to Teradyne’s J259 computer controlled system. Though archaic by today’s standards, it still was probably the first machine commercially available that was equipped with the roots of modern test technology. Like its competitor, it was a true software controlled system, not one with just a controller. It had a specially designed, 24 bit computer, preferred for instrumentation systems of the day. With one leg in the past and one in the future, it still used as I/O a teletype and card reader. But on the plus side it used a magnetic tape drive and a hard disc. Imagine the disk, 26 inches in diameter, with a 4 ft by 8 inch footprint. It stored all of 75,000 bits and the storage costs were about 33 cents per bit. Another feature was a small 4 bit shift register at the front of the test code registers for sync alignment—common practice in today’s systems. The system had a much improved speed, operating at the very high speed of 286 kbps.
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