ASH OS

Overview

A custom lightweight operating system built from scratch in C and x86-64 assembly, with kernel-level secure file access policies. Built with C, Assembly, x86-64.

The Problem

Understanding an operating system from documentation and source-reading alone only goes so far — writing a kernel forces you to confront boot sequencing, memory layout, and access control at the lowest level.

The Approach

• Wrote a custom bootloader and kernel in C and x86-64 assembly, without relying on an existing OS framework.
• Optimized the boot sequence for faster startup relative to a baseline unoptimized boot path.
• Implemented kernel-level file access policies to enforce secure access at the system level rather than in user space.
• Documented the architecture, kernel security model, and boot optimization approach, which became the basis of a published academic paper.

Key Engineering Decisions

What I Learned

Working below the OS abstraction layer changes how you reason about every layer above it — a lot of 'best practices' in application code exist to compensate for constraints you only see once you've written the kernel yourself.