NEC ACOS Series 77 System 600

These were announced in 1974 as the first large machines in the ACOS Series 77. Their product names were "ACOS Series 77, System 600 and 700", but they were known as the ACOS 600 and 700. The ACOS Series 77 large machines were developed based on the TOSBAC-5600, and attempted to deal with the difficult issue of upgrading the architecture while maintaining compatibility. Their features included: (1) MSI, which was a state-of-the-art technology at the time, (2) Cache memory in a multi-processor configuration, (3) A virtual memory system (with maximum program space of 64MB) employing distributed/dynamic main memory management based on the segmentation system and paging system, (4) A sophisticated access control system based on the domain protection system, (5) Comprehensive RAS design based on an online hardware self-diagnosis function, and (6) Shared libraries based on a shared segment mechanism.