A novel computer security authentication system is proposed to improve computer security. There are two main differences between the novel system and the conventional one. First, the key is a physical code that is stored in counter meshing gears (CMEs). Second, the user's password is discriminated by a microelectromechanical systems (MEMS) coded lock. This system is composed of a MEMS coded lock, a peripheral component interconnect (PCI) card with a printed circuit board (PCB), and software in a basic input/output system (BIOS) chip. Unlike the old MEMS coded lock, two reset micromotors and an optoelectronic coupler are installed in the new MEMS coded lock. The circuit of the PCI card with PCB, which is used to drive the four micromotors of the lock, is developed. The software is assembled by netwide assembler (NASM) and written into the BIOS chip. Testing of the prototype shows that the MEMS coded lock can discriminate the user's password effectively. If the user's password is matched with the physical code, permission to use the computer is granted; otherwise, it is locked up.