From the manual: The North Star Computers Z80A Processor Board (ZPB) provides Z80 microprocessor capability on the S-100 bus. The use of the Z80A chip allows full speed 4MHZ operation as a standard feature. The ZPB can be used in any standard S-100 bus computer and will operate in conjunction with nearly all other S-100 bus boards. ..... the ZPB contains the following features and options:

• AUTO-JUMP feature that will cause an automatic jump to any address at power-on or reset.
• VECTORED INTERRUPTS. ZPB logic will respond to eight levels of interrupt requests, determine the highest priority request pending and generate the appropriate RST instruction. The logic may be disabled to allow the function to be performed on another baord.
• FRONT PANEL INTERFACE for direct connection to IMSAI and other similar front panels.
• ADDRESS MIRROR feature to simulate the input/output characteristics of the 8080 microprocessor. This feature maintains compatibility with some S-100 peripheral boards.
• PROM OPTION. 1K of 2708 type erasable PROM can be added to the ZPB. This allows configuration of systems that require resident monitor and bootstrap programs. (Note: the PROM Option is not installed on this board).