(NOTE: not the same scale as the CPU ! The motherborad is a lot bigger !)
The mother board contains wiring to connect the CPU to other components of the computer:
Each pin signals a specific data, function or operation
Every signal pin has a signal name, e.g., MREQ (memory request), READ, etc
To signal a request, the manufacturer of the CPU can choose 0 or 1 value for that signal.
For example, the signal MREQ means "Memory Request", i.e., the CPU requests a transfer operation with the memory. The manufacturer of the CPU can choose
To denote the fact that MREQ = 1 to indicate that the CPU asserts the memory request, the MREQ signal is written on the spec (specification) sheet as:
On the other hand, if the manufacturer of the CPU decides that MREQ = 0 indicates that the CPU asserts the memory request, the MREQ signal is written on the spec sheet as:
You can see that some pins are asserted on high (such as INTR), while other pins are asserted on low (such as INTA) !!!
("Asserted" mean: "the function/request was activated")
We will discuss these pins next...
Control pins: (categorized)