Z80B (Z084006) 6.17MHz NMOS microprocessor made by Zilog. This is used in many arcade games and early home computers. This is a fast version.
Zilog Z08400x NMOS Speed Chart:
Z084002= Z80 at 2MHz
Z084004= Z80A at 4MHz
Z084006= Z80B at 6.17MHz
Z084008= Z80H at 8MHz
These have all been tested and verified NMOS in a Z80 Tester. See images below. These came from working arcade game boards.
Datasheet
