In fact, this is the best place to start reading the Nachos code, since this is where it all begins. Note that noff.h in this directory is a link to the file noff.h in userprog. All of the source code for the Nachos operating system, the machine simulation, and the test programs can be found here. The machine simulation. Except as noted in machine.h , you may not modify the code in this directory.
Nachos is a multi-threaded program.
Thread support is found here. The exception handling code is here, in exception.cc . Two different file system implementations are here. This can be changed by setting a flag in the Nachos makefile. Several independent simulated Nachos machines can talk to each other through a simulated network.