The TTL /MSI SN54 /74LS670 is a high-speed, low-power 4 x 4Register Fileorganized as four words by four bits. Separate read and write inputs, both addressand enable, allow simultaneous read and write operation.

The 3-state outputs make it possible to connect up to 128 outputs to in creasethe word capacity up to 512 words. Any number of these devices can beoperated in parallel to generate an n-bit length.

TheSN54/74LS170 provides a similar function to this device but it features open-collector outputs.