Complex sentence: Batch processing was really a methodological development on top of the earliest systems; computers still ran single programs for single users at any time, all that batch processing changed was the time delay between one program and the next.
Split into simpler sentences: Batch processing was effectively a methodological development on top of the earliest systems. Since computers still ran single programs for single users at any time, the primary change with batch processing was the time delay between one program and the next.