Page "CDC 6600" Paragraph 34

All but the first seven CDC 6000 series machines could be configured with an optional Extended Core Storage ( ECS ) system.

ECS was built from a different variety of core memory than was used in the central memory.

This made it economical for it to be both larger and slower.

The primary reason was that ECS memory was wired with only two wires per core ( contrast with 5 for central memory ), Because it performed very wide transfers, its sequential transfer rate was the same as that of the small core memory.

A 6000 CPU could directly perform block memory transfers between a user's program ( or operating system ) and the ECS unit.

Wide data paths were used, so this was a very fast operation.

Memory bounds were maintained in a similar manner as central memory — with an RA / FL mechanism maintained by the operating system.

ECS could be used for a variety of purposes, including containing user data arrays that were too large for central memory, holding often-used files, swapping, and even as a communication path in a multi-mainframe complex.