Operating-System

O.S. course data in NSYSU (National Sun Yat-sen University).

This repository contains four programming assignments from the Operating System course. Each assignment focuses on a different core OS concept implemented on Minix3 or as a standalone C/C++ program.

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pro_HW1 — Custom Shell (Basic)

Files: shell.c, testfile.txt, Programming Assignment 1.pdf, ReadMe.txt

A Unix-like shell implemented in C, designed to run on Minix3. The shell supports the following built-in commands:

Command	Description
exit	Terminate the shell
cd	Change the current directory
pwd	Print the current working directory
history [n]	Display the last n commands used (default: all)
help	Display the list of supported commands
NSYSU	Print an introduction to NSYSU
rabbit	Display an ASCII-art rabbit

In addition to built-in commands, the shell supports standard Minix3 commands and the following shell operators:

• & — Run a command in the background
• > — Redirect stdout to a file (overwrite)
• >> — Redirect stdout to a file (append)
• | — Pipe the output of one command into another

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pro_HW2 — Kernel Process Scheduling (Minix3)

Files: proc.c, proc.h, system.c, clock.c (inside sub-folders 1/ and 2/), Programming Assignment 2.pdf, DesignDocument.pdf, ReadMe.txt

This assignment involves modifying the Minix3 kernel to experiment with process scheduling and priority management. There are three sub-problems:

• Problem 1 (1/): Modify the kernel scheduler (proc.c, proc.h, system.c) to observe process priorities. After rebooting, use top to examine system performance.
• Problem 2 (2/): Apply an alternative proc.c with different scheduling behaviour, rebuild the kernel, and compare performance with Problem 1.
• Problem 3: Combines the kernel patches from either sub-problem with a modified clock.c that periodically prints the number of processes at each priority level to the screen. The system is accessed via SSH remote connection.

To apply any sub-problem, copy the relevant kernel source files to /usr/src/minix/kernel, rebuild and reinstall the kernel, then reboot and select option 2 at startup.

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pro_HW3 — Custom Shell with Shared Memory

Files: shell.c, Programming Assignment 3 v3.pdf, DesignDocument.pdf, ReadMe.txt

An extended version of the HW1 shell that adds multi-process and shared memory support. All original HW1 built-in commands and shell operators are retained.

New behaviour:

• When the shell is started with a numeric argument (e.g., ./shell 3), it spawns that many child processes.
• Any unrecognised command is written to shared memory and repeated across all child processes, demonstrating inter-process communication via shared memory.

Build & run:

clang shell.c -o shell
./shell 3   # spawn 3 child processes

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pro_HW4 — Disk Scheduling Algorithms

Files: DiskSchedulingAlgorithms.cpp, out.txt, Programming Assignment 4 (mod) v2.pdf, DesignDocument.pdf, ReadMe.txt

A C++ (C++17) simulation of classic disk scheduling algorithms on a disk with 5,000 cylinders and 1,000 random I/O requests. The program:

1. Displays all randomly generated request positions (cylinder number and location).
2. Prompts the user to enter the initial head position (0–4999).
3. Outputs the total head movement (number of cylinders traversed) and average latency (ms) for each scheduling algorithm.
4. Accepts -1 as input to terminate; upon exit, prints the average latency across all test cases.

Scheduling algorithms implemented:

Algorithm	Description
FCFS	First-Come, First-Served — processes requests in arrival order
SSTF	Shortest Seek Time First — services the nearest cylinder request first
SCAN	Moves the head in one direction, servicing requests, then reverses at the disk end
C-SCAN	Like SCAN, but the head returns to the start after reaching the far end (circular)
LOOK	Like SCAN, but reverses at the furthest pending request instead of the disk end
C-LOOK	Like C-SCAN, but jumps back to the nearest pending request instead of the disk start

Sample output is provided in out.txt.

Note: Compile and run with Visual Studio or a compatible C++17 compiler. Avoid DEV-C++.

Build example (Visual Studio command line):

cl /std:c++17 DiskSchedulingAlgorithms.cpp