The VAX 4000 Model 400, code-named "Omega", used the KA675 CPU module containing a 63 MHz (16 ns) NVAX microprocessor with 8 KB of on-die primary cache, 128 KB of external secondary cache.
The VAX 4000 Model 600, code-named "Omega/N +", is a distributed server positioned as a high-end VAX 4000 system introduced on 7 July 1992. It used the KA690 CPU module containing an 83MHz (12 ns) NVAX microprocessor with 10 KB of on-die primary cache and 512 KB of external secondary cache.