15.8. Execution Example and Time Calculation

Now, in this particular frame work now we are going to see how we are going to executive a Computer program.

So, we know that while going to execute an Instruction that Instruction Cycle is having basically 2 phase mainly 2 phase. One is your Fetch, second one is Execute.

The fetch and execute cycle is essential in understanding how a computer program runs. When we execute a program, the instruction cycle can be divided into two main phases: 'Fetch' and 'Execute'. In the 'Fetch' phase, the CPU retrieves an instruction from memory. This instruction is then processed in the 'Execute' phase, where the CPU performs the operation defined by the fetched instruction. Thus, both phases are vital for a seamless execution of a program.

Think of it like a chef following a recipe. The chef first fetches the required instruction (or step) from the recipe book. After understanding what to do, the chef executes that step, such as chopping vegetables or boiling water. Only when the current step is completed does the chef fetch the next step.

Now, here I am giving an example of a program. Here I have just mentioned or presented something over here in some tabular form. ... these 3 rows means we are going to execute 3 Instruction and in every row we are having 2 columns. So, these 2 columns indicate basically the execution phase of this particular Instruction.

In this example program executed by the CPU, we represent instructions in a tabular form. Each row corresponds to an instruction, and each instruction has two phases: fetching the instruction from memory and executing it. The first row shows the application of the 'Fetch' and 'Execute' phases. This structured representation helps us understand how the CPU processes multiple instructions sequentially.

Imagine a factory assembly line where each worker has a specific task to perform. Each row in the table represents a worker's task. The worker first grabs their task (fetching) and then performs it (executing). In the end, each worker passes on the product (result) to the next worker in line.

Now what this Instruction mean 1940? We don’t know. We have to see now what exactly we are going to do. Now it says that after performing this particular Instruction then what will happen...

The instruction '1940' is significant as it contains specific operation codes and memory addresses essential for the execution process. The operation indicates the task to be performed, while the address specifies where to find the operands. By decoding the instruction, the CPU understands how to manipulate data and which memory locations to access for inputs. This breakdown is critical for executing complex tasks efficiently.

Consider receiving a package with a shipping label that has instructions. The label contains both the type of delivery (operation) and the address where it needs to go (memory address). Only by understanding both can the delivery service successfully transport the package to the correct destination.

So, see now if I look into it you just see that we are storing our Instruction in Memory location 300, 301 and 302; that means, we must start our execution from the Memory location 300.

The Program Counter (PC) is a critical component of CPU architecture as it holds the memory address of the next instruction to be fetched for execution. In this example, instructions are stored in consecutive memory locations starting from 300. The PC initially points to 300, indicating that this is where instruction fetch will begin, guiding the CPU through program execution in an orderly manner.

Think of the Program Counter like a bookmark in a book. When you open the book to read, the bookmark shows you the page number where you left off. Just like a bookmark directs you to where to read next, the PC tells the CPU which instruction to fetch next in sequence.

So, during execution, you see what is happening it is showing the error. ... Now, according to that what will happen? Now the execution step of this particular Instruction will also be similar.

The execution of instructions involves clock cycles, which are fundamental timing units for processing operations. The processing of each instruction requires a series of clock cycles for both the fetch and execute phases. In this section, we see how many clock cycles it takes to complete each instruction, showing the intricacies involved in executing programs.

Think of clock cycles like the beats of a drum in a musical piece. Just as musicians must keep in time with the beats to play harmoniously, the CPU relies on clock cycles to ensure each instruction is executed correctly in the right sequence without missing any steps.

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