It's also in the DX register (DH specifically) after reset. Earlier CPUs did not have CPUID, so that's what the BIOS most likely used. "DX holds a component id

It's also in the DX register (DH specifically) after reset. Earlier CPUs did not have CPUID, so that's what the BIOS most likely used. "DX holds a component identifier and revision number after RESET as Figure 10-1 illustrates. DH contains 3, which indicates an 80386 component."