Web Resources for CS3650
(Computer Systems)
Final exam: Wednesday, Dec. 1:
The final exam is closed book, closed notes, and closed Internet. To access ostep.org or xv6, you may come to the front of
the room and briefly use my computer.
(And there will also be a final quiz on Dec. 8.)
(ADDED FOR FALL, 2021 ONLY:
Since the university was unable to assign us a time slot for a
final during finals week, our final exam will be on Monday,
Nov. 29. The final exam will be 30% of the course grade.
In addition, there will be a quiz on the last day of classes, Dec. 8,
worth 10% of the course grade.)
NOTE:
The office hours are as stated on the syllabus
(Mon. and Wed., 4:30 - 5:30; for Fall, 2021),
and by appointment. I am typically still in my office at least until 6pm.
Course basics:
Here are some immediate resources in the course for doing homework, following
the readings, etc.
- Course home:
- The course materials will always be available either from this web page or
from the course directory on the Khoury Linux computers: /course/cs3650/.
- Linux:
- The course is based on Linux (the third of the three popular
operating systems). If you do not yet have a Khoury Linux account, get one.
If you are not fluent in the basics of Linux/UNIX,
please go to any of the good tutorials on the Web.
Personally, I like:
*** this Linux tutorial *** (from M. Stonebank,
U. of Surrey, England), or this
*** updated one
for Linux/bash *** (by C. Tothill)
Other useful tips on Linux:
- Productivity tip: In most settings: the four cursor keys work
(for editing the current or previous commands);
and the <TAB> key works (for auto-completion of filenames and commands).
- If you're using Apple (the second most popular operating system), the
terminal window provides you with a UNIX-like environment.
- If you're using Windows (the most popular operating system), you can
install WSL2 (Windows Subsytem for Linux, version 2).
This gives you a Linux virtual machine side-by-side with Windows.
If you are unsure of which Linux distribution to use, Ubuntu is
a common first choice for those unfamiliar with Linux.
(When I followed the instructions for WSL2, I got
Error 0x1bc and I fixed it by downloading
the MSI package listed here. I then needed to enter "Windows
Features" in the search bar, and then select "Windows Hypervisor
Platform", and then go back to following the Microsoft
Windows instructions. Some people may also need to
turn on virtualization in their BIOS. After entering BIOS,
examine all options in all tabs with the letter 'v'. For me,
the option was "AMD SVM".)
(Another option is Ubuntu
Multipass, which requires VirtualBox, not necessarily
compatible
with WSLs's use of Hyper-V. And here is a good
article on installing the full Linux desktop for WSL2.
However, once WSL2 grabs RAM for the desktop, it seems to not want
to give it back to the rest of Windows. So, you'll want to
limit RAM for WSL2 as in the guide.)
-
In order to copy files between Windows and WSL, I create a link
inside WSL to the 'Downloads' folder:
cd
ls /mnt/c/Users
# For me, I am user 16176 in Windows. So, I type:
ln -s /mnt/c/Users/16176/Downloads ./
# You can now copy (cp) between ~/Downloads and ~ in WSL,
# where '~' is the Linux shortcut for your home directory.
- But if you insist on not using WSL2, then please try
putty
(substitute for 'ssh') and
WinSCP (substitute
for 'scp').
- Regardless of whether you are using Linux, Apple, or Windows/WSL2
on your laptop, practice using
ssh USERNAME@login.ccs.neu.edu
and
scp myfile.txt USERNAME@login.ccs.neu.edu:
(and notice the final colon with the 'scp' command line).
For help, try:
man ssh
and man scp
.
- Syllabus:
- The syllabus
contains the required readings in the textbook. It's available
from the link or from /course/cs3650/ (the course directory)
on Khoury Linux computers. Note especially our online
textbook ostep.org.
- Homework:
- The homework subdirectory
of the course directory contains all course homework,
and the course directory contains all handouts.
- Help directory:
- The course directory includes a help directory.
There are two older reviews of UNIX there.
But please consider this
excellent modern introduction to UNIX by M. Stonebank.
(or alt,
with updates to Linux/bash by C. Tothill)
- Linux editors:
- Please also note the directory for
UNIX (Linux) editors.
On Khoury Linux, try:
cd /course/cs3650/unix-editors. The editor vi
is a popular choice. To learn vi (estimated time: one hour),
login to Khoury Linux and do:
vi /course/cs3650/editors-unix/vitutor.vi
and follow the on-screen instructions.
- MIPS assembly language:
- The assembly portion of the course will be based on MIPS.
Please download the MARS Simulator for use with
MIPS assembly.
You can find the textbook's
"Green Card" online. You can find a manual for MIPS as
Appendix A in the textbook or else
Appendix A online. Read this, and re-read it.
The latter may require your Khoury Linux password.
Some other possibly useful resources from the web are
this quick reference sheet and this old introduction to the MARS Simulator.
The course will also heavily use the MIPS simulator.
- Common Linux Commands:
- Here is one web site
(Common Linux Commands)
with about 30 common Linux commands. If you haven't used Linux
much, try a quick review of these commands (passive knowledge
only). If you need more, there are plenty of great text and
video tutorials on the Linux command line.
- C language:
- We will briefly review the C language (the core of Java, but including
primitive types, only). For a more extensive overview of C, consider
a good, free
on-line C book by Mike Banahan, Declan Brady and Mark Doran.
- GDB debugger, gcc compiler, etc.:
- Some help files for Linux and its compilers,
editors, etc. are also available.
As you use Linux, please especially practice using GDB
(GNU debugger). This will help when you test your homeworks under Linux.
It will also reward you with more productive debugging for the rest of
your computer science career.
- Python
- See materials on Python,
and the Python subdirectory
- UNIX xv6
- The original UNIX was small enough that one can read all
of the code, with the right guidance. The
UNIX xv6 subdirectory has an easy-to-read
hyperlinked version of UNIX xv6, with about 7,000 lines of code
(about 100 pages of code).
- Thread synchronization
- "thread-synch" subdirectory
(notes on basic use of mutex, semaphore and condition variables)
- Undergraduate tutoring:
- Khoury College used to offer free undergraduate upper-class tutoriing.
I don't see a link to it right now (as of Sept., 2021).
If someone knows more about the current status of this resource,
tell me, and I'll update a link to it.
Going beyond: enrichment material:
- Some students have asked about a book for a more advanced introduction
to Linux and systems programming. This book goes well beyond what is
needed for the course. But for those who are interested, there is:
Advanced UNIX Programming, by Marc J. Rochkind
(free online access through
library.northeastern.edu)
- If you're interested in reading the original UNIX research paper, which
announced the implementation of UNIX to the world, see
The UNIX Time-Sharing System (1974).
-
Lecture on Parallel Computing (read the first half only, for
a nice overview and graphs of why multi-core is necessary, and
the benefits of many-core)
Texts for second half of course:
- Online text: ostep.org
(The final will cover all of the chapters on concurrency;
and also the chapters on files
from "Files and Directories" through "Fast File System (FFS)":
superblock, inode, etc. --- you do not
need to read about I/O Devices, disk drives and disk arrays.)
-
xv6-rev8.pdf:
UNIX xv6 (hyperlinked):
OR MAYBE:
UNIX xv6 (hyperlinked): (systems team re-organizing
our web directories?)
xv6 source code for UNIX kernel: especially see:
proc.c,h (process table);
swtch.S (context switch to a new process);
spinlock.c,h (spinlock, like a mutex);
file.c,h (file descriptor pointing to an open file);
fs.c,h (filesystem using superblock, inode, etc.);
pipe.c,h (pipes: e.g., ls | wc
);
bio.c,h (buffered I/O: linked list of buffers acting as a cache
for disk blocks or disk sectors).
If you are curious, you can also read about the
history of xv6.
-
Book with commentary on xv6-rev8 (UNIX kernel)
- Python (based on materials in
/course/cs3650/python)
-
Early history of Python (just for fun)
MIPS Simulator for Assembly Language homework (MARS):
- There is a
MIPS Assembly language simulator with
free downloads available and
online documentation. For your convenience, a copy of
the simulator is at: MIPS-simulator.
There is also an
online video demo of the Mars simulator.
- To begin running the simulator, go inside the folder, and
double-click on the Mars.jar icon. Alternatively, if running
from the command line in Linux, type:
java -jar Mars.jar
If you download Mars.jar for your computer, there are also
suggestions on that page for running Mars.
- The syntax of the assembly language is intended to be compatible
with Appendix B of our textbook (also
available online
(requires CCIS password)).
- The software is distributed as a Java .jar file. It requires
Java J2SE 1.5 or later. Depending on your configuration,
you may be able to directly open it from the download menu.
If you have trouble, or if you prefer to run from the
command line on your own computer, the Java SDK is is also available
for free download from the same download page. The instructions
for running it from Windows or DOS should work equally well
on Linux. The CCIS machines should already have
the necessary Java SDK installed.
- GOTCHAS: There are several important things to watch out for.
- When you hit the "Assemble" menu item, any error messages about
failure to assemble are in the
bottom window pane, tab: "Mars Messages".
Input/Output is in the bottom window pane, tab: "Run I/O"
- If you paste assembly code into the edit window pane, you must
save that code to a file before Mars will let you assemble it.
- If you have selected a box with your mouse (e.g. "Value" box in
the data window pane, or "Register" box), then Mars will not
update the value in that box. Mars assumes you prefer to write
your own value into that box, and not to allow the assembly
program to use that box.
- If your program stops at an error, read the "Mars Messages" for
the cause of the error, and then hit the "Backstep" menu item
to see what caused that error. Continue hitting "Backstep"
or "Singlestep" in order to identify the error.
- Your main routine must call the "exit" system call to terminate.
It may not simply call return ("jr $ra"). Note that page B-44
of Appendix B of the text (fourth edition) has a table of
"system services" (system calls). These allow you to do "exit"
and also I/O.
- One of the nicer features of this software is a limited
backstep capability (opposite of single-step) for debugging.
In addition, the help menu includes a short summary
of the MIPS assembly instructions.
In general, I like this IDE for assembly even better than some
of the IDEs that I have seen for C/C++/Java.
(The one feature that I found
a little unintuitive is that if you want to look at the
stack (for example) instead of data, you must go to the
Data Segment window pane, and use the drop-down menu at the
bottom of that pane to choose "current $sp" instead of ".data".)
- Please note the
three sample assembly programs, along with an accompanying
tutorial on the same web page.
- I'd appreciate if if you could be on the lookout
for any unusual issues, and report them promptly (along with
possible workarounds), so the rest of the class can benefit.
Thanks very much for your help on this.

GDB (GNU DeBugger):
A Few Simple Debugging Commands Save You Hours of Work
INVOKING gdb:
gdb --args
Example: gdb --args ./a.out
COMMON gdb COMMANDS:
BREAKPOINTS: break, continue
STARTING: break main, run
WHERE AM I: info threads, thread 1; where, frame 2; list
PRINT: ptype, print ( ptype argv[0]; print argv[0] )
EXECUTING: next, step, finish, continue
(next line, step inside fnc, until previously
unseen line (escape a loop), finish current fnc,
continue to next breakpoint)
EXIT: quit
< Cursor keys work, TAB provides auto-complete >
PARENT AND CHILD PROCESSES:
set follow-fork-mode child
(after call to fork(), switch to debugging child process)
DEBUGGING INFINITE LOOP:
run; TYPE ^C (ctrl-C) TO TALK TO gdb; where; print var1; etc.
HELP: help e.g.: (gdb) help continue
ADVANCED gdb: USING gdbinit:
In a more sophisticated debugging session, you may have to try
multiple GDB sessions. To do this, you will want to try doing:
gdb -x gdbinit --args ./a.out myargs
First, create a dbinit file. An easy way is, in your last GDB session,
(gdb) show commands
Then copy-paste those comamnds into gdbinit. Then at the top of
gdbinit, insert:
# gdb -x gdbinit --args ./a.out myargs [Customize as needed]
set breakpoint pending on
set pagination off
# Stop if about to exit:
break _exit
# Continue w/ output of 'show commands'; Extend and modify as needed
MORE ADVANCED gdb:
info function
IF DEBUGGING C++ CODE, you will find this useful, in order
to discover the full GDB name of your target method.
macro expand MACRO_FNC(ARG)
debugging after fork:
set detach-on-fork off
break ...
run
info inferiors
EXTENDED "WHERE AM I":
info inferiors; inferior 2
info threads; thread 1
NOTE: The qualified thread number is: .
So, 'thread 2.3' switches to thread 3 in inferior 2.
where; frame 2
list; print myvariable
For digging deeper into GDB, try:
"gdb - customize it the way you want".
NOTE: For those who like a
full-screen display of the current code, try the command
^Xa
(ctrl-X a) to turn full-screen mode on and off. Also, try:
(gdb) layout split
NOTE: For those who like to try a
reversible version of GDB, see
rr-project.org
(for GDB with reverse execution)
NOTE: For a _really cool_
GDB interface, look at: https://github.com/cyrus-and/gdb-dashboard. To try it out,
just go to the .gdbinit file from that web site, and then copy
the code into a local file,
gdbinit-dashboard,
and then execute
source gdbinit-dashboard
in GDB. Personally, I like to use Dashboard by
displaying the whole dashboard in another terminal.
Python
There are some good introductory materials for Python in
the instructor's directory.
After trying those out, here are some other Python background
materials:
Python
NEWS (from Fall, 2021 and earlier):
Current Events
NEWS (from 2022 and earlier):
SPECULATION ABOUT FUTURE CHIPS
AND THE END OF MOORE'S LAW:
(Many of these articles
are from digitimes.com.)
For context, note the
Wikipedia Silicon article
on the covalent radius
of silicon is 0.111 nm. So, the distance between adjacent silicon atoms
is the diameter (0.222 nm).
7 nm is approximately 31.5 silicon atom diameters.
5 nm is approximately 22.5 silicon atom diameters.
3 nm is approximately 13.5 silicon atom diameters.
2 nm is approximately 9.0 silicon atom diameters.
- NEWS (July 19, 2022):
Competition in 3nm smartphone AP market to take place in 2H23
- NEWS (July 12, 2022):
Volkswagen constructing first in-house battery plant in Europe,
considering 'big moves' in China
- NEWS (Apr. 21, 2022):
US bid to boost chipmaking to be expensive and wasteful,
says TSMC founder Morris Chang
- NEWS (Feb. 21, 2022):
Global chipmakers find ways to improve competitiveness
($440B, $380B, and $280B capital expenditures in 2022
by TSMC, Samsung and Intel)
- NEWS (Jan. 19, 2022):
Intel is on track to adopt 0.55 High-NA EUV lithography in 2025
("NA" is "numerical aperture"; or alt or alt2)
- NEWS (Dec. 7, 2021):
The Great Tech Rivalry: China vs the U.S.
(by Avoiding Great Power War Project at Harvard University's
Belfter Center;
while an excellent review
of technical progress in the U.S. and China, it unfortunately
does not review the fast rising technical progress in India)
- NEWS (12/24/21):
TSMC to move 3nm process to commercial production in 4Q22
- NEWS (12/23/21):
Autonomous delivery picking up in US
- NEWS (12/1/21):
TSMC enters pilot production of 3nm chips
- NEWS (10/8/21):
TSMC on track to ramp 3nm chip production (in second half, 2022)
- NEWS (8/31/21):
WHY THE GLOBAL CHIP SHORTAGE IS MAKING IT SO HARD TO BUY A PS5
(about the semiconductor supply chain)
- NEWS (8/18/21):
Samsung unlikely to move 3nm GAA process to volume production until 2023
- NEWS (7/2/21):
Micron to adopt EUV in DRAM manufacturing by 2024
- NEWS (4/16/21):
TSMC to boost 5nm chip output in 2H21
- NEWS (4/8/21):
Microsoft unveils liquid cooling solution for datacenters
- NEWS (3/26/21):
Ball screws with smart maintenance)
- NEWS (12/15/20):
TSMC to see 20% rise in 5nm shipments in first half of 2021
- NEWS (12/2/20):
TSMC to roll out 3nm Plus process in 2023
- NEWS (10/16/20):
TSMC expects 5nm chip sales to boost in 2021
Hiwin develops EV-use smart ball screws
(another source of high demand for CPU chips:
Ball screws with smart maintenance)
- NEWS (3/24/21):
Intel announces US$20 billion fab expansion plans in foundry revamp
- NEWS (3/17/21):
Micron to shift resources from 3D XPoint to CXL memory
(Definintions:
CXL: Compute-Express Link; 3D XPoint (aka Optane memory);
CDI: Composable disaggregated infrastructure)
- What is composable infrastructure?
("One workload could be a compute-heavy application requiring a lot
of CPU power, while another could be memory-heavy. The application
can grab whatever it needs at the time that it runs, and when it¿s
done, it returns it to the pool.")
- CXL initiative tackles memory challenges in heterogeneous computing
("In CXL, we start with CPUs, with cacheable memory both North and
South, both to its own memory and to the accelerator memory. Those
two pools would be part of the coherent memory pool addressable by
both machines." ... "In a data center, CXL operates primarily at the
node-level layer .... For the rack and row levels, the open systems
Gen-Z interconnect can provide memory-semantic access to data and
devices via direct-attached, switched or fabric topologies." ...
"CXL and Gen-Z are very complementary.")
- NEWS (2/26/21):
Highlights of the day: TSMC expanding 5nm capacity
- NEWS (10/8/20):
TSMC likely to make another upward adjustment to capex outlook
... due to strong demand for 7nm and 5nm
- NEWS (9/24/20):
TSMC mulling more 2nm capacity
- NEWS (9/21/20):
TSMC reportedly adopts GAA transistors for 2nm chips
- NEWS (7/27/20):
Intel may expand partnership with TSMC (7nm chips)
OLDER NEWS from Spring, 2015:
NEWS:
Talk by Yale Patt (famous researcher
in Computer Architecture)
NEWS:
2015 CCIS Colloquia (research talks by invited guests to CCIS: topics including security, big data, social networks, robotics, natural language, etc.)
NEWS:
Android Apps that Never Die (talk by me, Gene Cooperman, and Rohan Garg, at ACM undergrad chapter: 6 p.m., Wed., Feb. 25, 104 WVG) (pizza included)
NEWS:
One VLSI fabrication facility: $6.2 billion as of 2014
(from digitimes.com):
UMC to build 12-inch fab in Xiamen
(Many of these articles
are from digitimes.com.
For context, note the Wikipedia Silicon article on the covalent radius of silicon is 0.111 nm. So, the distance between adjacent silicon atoms is the diameter (0.222 nm).
10 nm is approximately 45 silicon atom diameters.
5 nm is approximately 22.5 silicon atom diameters.
3 nm is approximately 13.5 silicon atom diameters.)

- TOP500 Supercomputer Sites
- NOTE: This writing is as of Fall, 2021. (Things change quickly
in this area.) In terms of CPUs, we are in a three-way race
among chips from Intel, AMD, and ARM (but also the IBM Power9
CPU chip on supercomputers, such as the
Summit supercomputer).
In the past, it was
between Intel and AMD. The current largest supercomputer
is
Fugaku in Japan, based on 7~nanometer ARM chips (with no GPUs).
China's upcoming
Tianhe-3 supercomputer will also be based on ARM.
Similarly, the
Apple M1 chips are based on A64 ARM (with 4 big and 4 little
cores). Most of the remaining top supercomputers are based
on Intel or AMD, and often include NVIDIA GPUs on each node.
Intel will soon be offering CPUs with discrete
Intel Xe GPU chips, also to be included in the upcoming
Aurora supercomputer. Meanwhile, the upcoming
El Capitan supercomputer
will be based on AMD CPUs and AMD GPUs, and will be used
especially by the National Nuclear Securitay Administration
(NNSA) for numclear weapon modeling.
- Lists of Top 500
supercomputers in the world, with Top 10 on first page.
- Some recent blogs from the TOP500 site:
-
El Capitan, Frontier, and Aurora: exascale supercomputers
(appearing from 2021--2023; see especially the table, lower down
in this article)
Deep Learning (a motivator for high-end HPC):
Deep Learning on NVIDIA GPUs
DeepMind Beats Human Champion at Game of Go
(in 2015)
"[The
deep learning algorithm of] AlphaGo doesn't actually use that much
hardware in play, but we needed a lot of hardware to train it and do all
the different versions and have them play each other in tournaments on
the cloud. That takes quite a lot of hardware to do efficiently, so we
couldn't have done it in this time frame without those resources."
Relative Popularity of Different Languages
Benchmark Games (Which is faster, C, Java, or Python?):
(Benchmarks are notoriously variable. Be careful about how you interpret this.)
Three Newer Languages (with lessons from Scheme/Java/C/C++)
- Go (widely used at Google;
also the source language for
Docker,
a new type of lightweight virtual machine built on
top of Linux containers)
- Rust (grew out
of Mozilla, the developer of Firefox; may be used for a future
version of Firefox)
- Scala (runs on JVM;
Spark, a proposed successor to Hadoop, is built using Scala,
and supports Scala, Java, and Python)

A Few Simple Debugging Commands Save You Hours of Work
INVOKING gdb:
gdb --args
Example: gdb --args ./a.out
COMMON gdb COMMANDS:
BREAKPOINTS: break, continue
STARTING: break main, run
WHERE AM I: info threads, thread 1; where, frame 2; list
PRINT: ptype, print ( ptype argv[0]; print argv[0] )
EXECUTING: next, step, finish, continue
(next line, step inside fnc, finish current fnc, cont. to next breakpoint)
EXIT: quit
< Cursor keys work, TAB provides auto-complete >
PARENT AND CHILD PROCESSES:
set follow-fork-mode child
(after call to fork(), switch to debugging child process)
DEBUGGING INFINITE LOOP:
run; TYPE ^C (ctrl-C) TO TALK TO gdb; where; print var1; etc.
HELP: help e.g.: (gdb) help continue
ADVANCED gdb:
info function
IF DEBUGGING C++ CODE, you will find this useful, in order
to discover the full GDB name of your target method.
macro expand MACRO_FNC(ARG)
debugging after fork:
set detach-on-fork off
break ...
run
info inferiors
EXTENDED WHERE AM I:
info inferiors; inferior 2
info threads; thread 1
where; frame 2
list; print myvariable
For digging deeper into GDB, try "gdb - customize it the way you want".
NOTE: For those who like a
full-screen display of the current code, try the command ^Xa (ctrl-X a)
to turn full-screen mode on and off.
NOTE: For those who like to try a reversible version of GDB, see
rr-project.org
(for GDB with reverse execution)
There are some good introductory materials for Python in
the instructor's directory.
After trying those out, here are some other Python background
materials:
Python
The following note by Rob Landley
is a truly excellent summary of the most important points of
virtual memory as it's really used (not just the textbook theoretical
synopsis):