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This is an archived course. A more recent version may be available at ocw.mit.edu.
Lectures: 2 sessions / week, 1.5 hours / session
6.828 teaches the fundamentals of engineering operating systems. You will study, in detail, virtual memory, kernel and user mode, system calls, threads, context switches, interrupts, interprocess communication, coordination of concurrent activities, and the interface between software and hardware. Most importantly, you will study the interactions between these concepts, and how to manage the complexity introduced by the interactions.
To master the concepts, 6.828 is organized in three parts: lectures, readings, and a major lab. The lectures and readings familiarize you with the main concepts. The lab forces you to understand the concepts at a deep level, since you will build an operating system from the ground up. After the lab you will appreciate the meaning of design goals such "reducing complexity" and "conceptual integrity".
The lectures are organized in two main blocks. The first block introduces one operating system, xv6 (x86 version 6) , which is a re-implementation of UNIX® version 6, which was developed in the 1970s. In each lecture we will take one part of xv6 and study its source code; homework assignments will help you prepare for these lectures. At the end of the first block (about half-way the term), you will understand the source code for one well-designed operating system for an Intel-based PC, which help you building your own operating system.
The second block of lectures covers important operating systems concepts invented after UNIX® v6. We will study the more modern concepts by reading research papers and discussing them in lecture. You will also implement some of these newer concepts in your operating system.
You may wonder why we are studying an operating system that resembles UNIX® v6 instead of the latest and greatest version of Linux®, Windows®, or BSD UNIX®. One reason is that v6 is simple and small, but contains the important concepts and clean organization of modern Unixes. Many modern UNIX® versions have an internal structure identical to v6 and many of their data structures are still named as in v6, but are cluttered with additional features. Furthermore, almost all modern operating systems have adopted ideas from v6 (including the C programming language). In short, because v6 is old, it doesn't mean it is irrelevant. (The laws of Newton are still relevant and Einstein's papers on relativity theory are still well worth reading too.)
xv6 is our re-implementation of v6 for an Intel x86-based multiprocessor. The reason we are studying xv6 instead of the original v6 code is that learning v6 requires understanding an arcane C and an out-of-date computer (PDP-11); xv6 follows the structure of v6, but is implemented for a modern x86-based multiprocessor.
The lab is the place where the rubber meets the road. In the lab you will internalize the details of the concepts and their interactions. For example, although you have seen virtual memory in 6.004, 6.033, and again in 6.828 lectures, you will soon discover, during the labs, that you didn't really understand virtual memory, and how it interacts with other concepts.
The lab is split into 6 major parts that build on top of each other, accumulating in a primitive operating system on top which you can run simple commands through your own shell. (We reserve the last lecture for you to demo your operating system to the rest of the class.)
The operating system you will build, called JOS, will have UNIX®-like functions (e.g., fork, exec), but is implemented in an exokernel style (i.e., the UNIX® functions are implemented mostly as user-level library instead of built-in to the kernel). The major parts of the JOS operating system are:
We will provide skeleton code for pieces of JOS, but mostly you will have to do all the hard work.
The first 5 assignments are done individually. The last assignment is a team assignment. The first set of assignments have design freedom in the details; the last assignments have a lot of design freedom. You will never be able to pattern match from xv6; you internalize the concepts by building similar functions in a radical different way.
You will develop your JOS operating system for a standard x86-based personal computer, the same one used for xv6. To simplify development we will use a complete machine simulator (Bochs) in the class for development and debugging. This simulator is real enough, however, that you will be able to boot your own operating system on physical hardware if you wish.
At the end of the lab you will be able to find your way around the source code of most operating systems, and more generally, be comfortable with system software. You will understand many operating systems concepts in detail and will adapt them to other environments. You will also understand the x86 processor and the C programming language well.
C, 6.033, and 6.170 (and, by implication, 6.004)
6.828 is primarily intended for seniors and MEng students who want to learn about operating systems in detail. PhD students are also welcome, but note that 6.828 is not a "core" subject for the TQE.
To turn-in the labs, send email to 6.828 staff with a URL pointing at your solutions. The email must be received by 11:59 pm on the day that the lab is due.
You are required to turn in each lab. Labs that are not turned in will receive an F. Labs that are turned in but score 0 points will receive a D. You have a total of 3 late days to use throughout the semester. There are no partial late days: an assignment that is only six hours late uses an entire late day. After you have used up your late days, each additional day late will incur a full letter grade penalty. Saturday and Sunday both count as days.
Our policy is simple, based on professional standards: On quizzes you should not collaborate. On all other assignments you are welcome to work with anyone else on ideas and understanding, but you should complete all assignments on your own, and you should carefully acknowledge all contributions of ideas by others, whether from classmates or from sources you have read.
Grades in 6.828 will be based on the results of two quizzes (one during the term and one in final's week, lab exercises, and homework assignments and class participation. The percentages of each activity are as follows:
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