Computer Organization and Assembly Language Lab CS-222L

LAB REPORT - 02
Computer organization and Assembly language Lab
Course Title: Computer organization and Assembly language
Lab Title: Programming with NASM and Linux System call

Name: Muhammad Salman

Presentation/Procedure Code Comments Response Total

1|Page
Computer Organization and Assembly Language Lab CS-222L

Tasks
Lab Task 1: Run Example 1
Save the file as a “hello.nasm” and execute

Output:

Procedure:
1. Start program with _start label.
2. Use eax = 4 for sys_write.
3. Use ebx = 1 for stdout.
4. Use ecx = msg for message address.
5. Use edx = 13 for message length.
6. Call int 0x80 to print message.
7. Use eax = 1 for sys_exit.
8. Use ebx = 0 for exit code.
9. Call int 0x80 to exit.

2|Page
Computer Organization and Assembly Language Lab CS-222L

Lab Task 2: Run Example 2

Output:

Procedure:
1. Start program with _start label.
2. Use eax = 4, ebx = 1, ecx = msg, edx = len to display prompt.
3. Call int 0x80.
4. Use eax = 3, ebx = 0, ecx = buffer, edx = 100 to read input.
5. Call int 0x80.
6. Use eax = 4, ebx = 1, ecx = buffer, edx = 100 to print input.
7. Call int 0x80.
8. Use eax = 1, ebx = 0, then int 0x80 to exit.

3|Page
Computer Organization and Assembly Language Lab CS-222L

Lab Task 3: Modify Example 1

Output:

Procedure:
1. Start program with _start label.
2. Define new message Welcome to Assembly Programming!.
3. Use eax = 4, ebx = 1, ecx = msg, edx = 30.
4. Call int 0x80 to print message.
5. Use eax = 1, ebx = 0.
6. Call int 0x80 to exit.

4|Page
Computer Organization and Assembly Language Lab CS-222L

Lab Task 4: Modify Example 2

Output:

Procedure:
1. Start program with _start label.
2. Use eax = 4, ebx = 1, ecx = msg, edx = len to display prompt.
3. Call int 0x80.
4. Use eax = 3, ebx = 0, ecx = buffer, edx = 50 to read input.
5. Call int 0x80.
6. Use eax = 4, ebx = 1, ecx = buffer, edx = 50 to print input.
7. Call int 0x80.
8. Use eax = 1, ebx = 0, then int 0x80 to exit.

5|Page
Computer Organization and Assembly Language Lab CS-222L

Comments;

• This lab exercise was a valuable introduction to the fundamentals of x86 assembly
language programming using NASM and Linux system calls.
• The tasks were structured in a way that gradually built up the learner’s understanding—
from printing a simple message to handling user input and modifying behavior based on
program logic.
• By directly working with system calls like sys_write, sys_read, and sys_exit, and using
registers such as eax, ebx, ecx, and edx, students experienced how arguments are
passed and how the processor communicates with the operating system.
• The hands-on nature of the lab helped in visualizing the flow of control at the machine
level, and the use of sections like .data, .bss, and .text illustrated how memory and
code are organized in assembly.
• The requirement to modify the existing code (e.g., changing the message or limiting
input size) encouraged critical thinking and gave students confidence to experiment with
assembly instructions.
• Overall, the lab effectively blended theory with practice, making abstract architectural
concepts more tangible and easier to grasp.

Conclusion;
In conclusion, Lab #02 served as an excellent stepping stone into the world of low-level
programming using assembly language. It achieved its goal of helping students understand
how a processor interacts with memory, handles input/output, and executes instructions
using system calls. Writing programs using NASM on a Linux environment gave a real-world
context to theoretical topics like CPU registers, memory segmentation, and system-level
programming. The experience of assembling, linking, and executing the code helped
students understand the complete lifecycle of a program, from source code to executable.
Moreover, tasks like modifying code and changing buffer sizes reinforced the importance
of precision and control that is unique to assembly language. This lab has laid a solid
foundation for future topics in computer architecture, operating systems, and embedded
system development by fostering a deeper appreciation of how computers operate at the
most fundamental level.

_________________END_______________

6|Page