After completing his PhD and some post-doc work, Slotnick ended up at IBM. By this time, for scientific computing at least, tubes and drums had been replaced with transistors and core memory. The idea of parallel processors working on different streams of data from a drum no longer had the same obvious appeal. Nevertheless, further consideration showed that parallel machines could still offer significant performance in some applications; Slotnick and a colleague, John Cocke, wrote a paper on the concept in 1958.