PRML (Partial-Response Maximum Likelihood) is a superior method of data detection now used universally in tape and disk drives. The first commercial use of PRML was in the Ampex DCRS (Digital Cassette Recording System) tape recorder in 1984. IBM introduced the technology in hard disk-drives in 1990. This 1982 prototype of the PRML detector card was designed by David Petersen, freshly graduated from University of Washington. Petersen worked under the guidance and direction of Roger Wood and Charles Coleman, the designer and lead engineer for DCRS. Coleman had come to fame in the invention of color video recording. DCRS was Ampex TM’ most successful digital product earning some $320 million over its lifetime.
The object is a circuit board mounted on a metal backplane. The metal front panel consists of two switches, a data and a clock connector, and a detector clock adjustment hole. Silkscreened onto the upper right corner is the designation, "DECODER NO. 3 (VITERBI DETECTOR). A handwritten label on the back reads, "AMPEX 'DCRS' PROTOTYPE 117 Mbit/sec 1982."