Complex sentence: By this time, for scientific computing, tubes and drums had been replaced by transistors and core memory, and the idea of parallel processors working on different streams of data from a drum no longer had the same obvious appeal.
Split into simpler sentences: By this time, for scientific computing at least, tubes and drums had been replaced by transistors and core memory.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.