A Road Map Through Nachos

Abstract:

Nachos is instructional software that allows students to examine, modify and execute operating system software. Nachos provides a skeletal operating system that supports threads, user-level processes, virtual memory and interrupt-driven input output devices. Nachos is a complex piece of software and it is difficult for beginning students (and instructors) to easily gain on overall understanding of the various system pieces and how they fit together.

This document provides a road map to understanding the Nachos system. It gives a high-level overview of the source code, focusing on the big picture rather than on the details. It is not intended as a replacement for reading the source code. Rather, it is a companion that is intended to help students (and instructors) overcome the initial learning curve encountered when learning and using the system.

• Contents
• Introduction to Nachos
• Nachos Machine
• Machine Components
• Interrupt Management
• Real-Time Clock Interrupts
• Address Translation
• Linear Page Tables
• Software Managed TLB
• Console Device
• Disk Device
• Nachos Threads
• Mechanics of Thread Switching
• Threads & Scheduling
• Synchronization and Mutual Exclusion
• Special Notes
• User-Level Processes
• Process Creation
• Creating a Noff Binary
• System Calls and Exception Handling
• Execution Trace of User-Level Process
• Nachos Filesystem
• SynchDisk
• FileSystem Object
• OpenFile Object
• File System Physical Representation
• File Header
• Directories
• Putting It All Together
• Experience With Nachos Assignments
• General Tips
• Synchronization
• Multiprogramming
• Virtual Memory
• File System
• Common Errors
• MIPS Architecture