System Bus Board; Central Processing Unit - Zenith Z-100 Reference Manual

As you can see, the main artery for system communication is the I/O bus, which
acts as the main trunk for information transfer. What is not readily apparent from
the block diagram, is that the CPU acts as the main traffic control element for
information flow.

Central Processing Unit

The CPU is really the operational heart of any computer system. The 8088 micro-
processor is the main decision-making element which keeps everything happening
at the right time. The 8088, the DMA controller, the program interrupt controller,
and three independent 16-bit timing counters make up the CPU subsystem in
your computer.
An optional 8087 coprocessor may also be installed in the system. This device
will take over the higher mathematical operations ordinarily performed by the
8088 under software, freeing the 8088 to other tasks, such as controlling informa-
tion flow. The main advantage of adding the coprocessor is an apparent increase
in speed of the CPU when running programs which can take advantage of it

System Bus Board

The 8-connector array on this card is basically an extension of the microprocessor
I/O bus, but demultiplexed, and enhanced by the addition of interrupts and DMA
functions. The bus interface is implemented via a 62-pin edge connector on the
card or device which plugs into one of the eight backplane sockets. The bus
supplies the following:
Eight bits of bidirectional data
Twenty address lines
Six interrupt levels
Control lines for memory and VO read and write
Clock and timing control lines
Channel check line for device error reporling or parity error reporting by
add-on memory
Operating power consisting of ~ 5 VDC, ~ 12 VDC, and ground
READY line for use by slow devices
Page 3.3
System Input/Output