The IBM System/370 (S/370) was a model range of IBM mainframe computers announced on June 30, 1970 as the successors to the System/360 family. The series mostly maintained backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the product announcement. Improvements over the S/360 first released in the S/370 model range included:

• The block multiplexor channels introduced on the most recent high end System/360 systems.
• standard dual-processor capability;
• "monolithic main memory" on the model 145, based on integrated circuits instead of magnetic cores; However, the larger models 155 and 165 still used core memory.
• full virtual memory through a new microcode floppy disk on the 370/145 and a hardware upgrade to include a DAT box on the 370/155 and 370/165; these were not announced until 1972;
• 128-bit (hexadecimal) floating point arithmetic on all models.