the journey of IAS

[logistic_guy]

On the IAS, describe in English the process that the CPU must undertake to read a value from memory and to write a value to memory in terms of what is put into the MAR, MBR, address bus, data bus, and control bus.

 

[logistic_guy]

Before we talk about the journey of this $\displaystyle \text{IAS}$, let us familiarize ourselves with some of the terms.

$\displaystyle \text{MBR} \rightarrow$ Memory Buffer Register

It can hold or store a word that can be either sent to or received from the memory or the $\displaystyle \text{I/O}$ unit.

 

[logistic_guy]

$\displaystyle \text{MAR} \rightarrow$ Memory Address Register

It stores the memory address where the specified word will be written to or read from.

 

[logistic_guy]

The $\displaystyle \text{address bus}$ carries memory locations.

 

[logistic_guy]

The $\displaystyle \text{data bus}$ carries the data being processed.

 

[logistic_guy]

The $\displaystyle \text{control bus}$ carries $\displaystyle \text{CPU}$ read/write signals and status signals.

 

[logistic_guy]

The whole idea of this $\displaystyle \text{IAS}$ is to read from the memory or to write to the memory. It needs instructions to do that, and these instructions are done in cycles. So it performs these instruction cycles in a repeating manner.

These instruction cycles consist mainly of two sub cycles:

$\displaystyle \text{fetch}$ and $\displaystyle \text{execute}$