How do computers execute programs?

How Do Computers Execute Programs?

Computers execute programs by following a sequence of instructions written in a programming language. These instructions are translated into machine code, which the computer's processor (CPU) can understand and execute directly.

Explanation

1. Source Code: Programs are written in high-level languages (like Python or C).
2. Compilation/Interpretation: The source code is converted into machine code (binary instructions) by a compiler or interpreted line-by-line by an interpreter.
3. Execution: The CPU fetches, decodes, and executes each instruction in the program, manipulating data in memory and performing calculations as needed.

The basic cycle the CPU follows is called the fetch-decode-execute cycle.

Worked Example

Suppose we have a simple program that adds two numbers:

``c
int a = 2;
int b = 3;
int sum = a + b;
``

Step-by-step execution:

4. Compilation: The code is compiled into machine instructions, such as:
• Load value 2 into register $R_1$
• Load value 3 into register $R_2$
• Add $R_1$ and $R_2$, store result in $R_3$
• CPU Execution:

For the addition step:

$$ R_3 = R_1 + R_2 = 2 + 3 = 5 $$

Now, $R_3$ holds the value $5$, which is the result of $a + b$.

Takeaways