An Integrated Approach to
Teaching Computing Systems
Architecture
Kishore Ramachandran
&
Bill Leahy
College of Computing
Georgia Institute of Technology
Outline
• Traditional approach
• Pedagogy of new approach
• Where does it fit and how do
we put it in practice?
• Experience at Tech
• Evaluating the pedagogy
• Challenges
• Comparison to other
pedagogical models
• Concluding remarks
Traditional Approach
• Stovepipe model
– Architecture and OS as
distinct courses usually in the
junior/senior years
• Georgia Tech
– Followed similar model until
1999
– Two junior level courses one
on OS and the other on
architecture
What is wrong with the traditional
approach?
• Symbiotic relationship missed
– High level language and
instruction sets
– OS abstractions and processor
– Network protocols and physical
network
– Students get this?
• Not if compartmentalized
• Gap between the time when
the courses are taken
– Concepts forgotten
• Connections not seen at all by
the students most of the time
Why change?
• Problems with the
traditional approach
• Changing CS scene
– New areas evolving
– Graphics, visualization, HCI
– Need rethinking of “core”
• UG research involvement
– Need to infuse interest early
– Entry level for systems
research high
New approach
• Excitement of middle-school
kids
– What is inside a box?
– What makes it play cool music or
video games?
• An integrated course
– Combining OS and architecture
• Goal of the course
– “Unraveling the box”
– Take the journey together
exploring hardware and the OS
abstractions
– Emphasize connectedness
Pedagogy of new approach
• Present what is “inside a
box”
–
–
–
–
–
Processor module
Memory module
I/O and storage module
Parallel module
Network module
• Key differentiator
– Concomitant treatment of
hardware and software in
each module
Pedagogical style
• Discovery as opposed to
indoctrination or instruction
• Top down approach
– Start with problem to be solved
– Explore solution space together
• Example:
– What is memory management?
• Understand the need first
• Discover the software issues and
the corresponding hardware issues
• Story telling approach
– Keeps the student interest alive
Processor module
• HLL constructs and their
influence on instruction-set
design
• Simple implementation
followed by performanceconscious pipelined
implementation
• Process abstraction in OS
and processor scheduling
Memory module
• Memory management in
OS
• Architectural issues
• Memory hierarchies
I/O and storage module
• Program discontinuities
including interrupts, traps,
and exceptions
– Processor mechanisms
– OS mechanisms
• Devices and device drivers
• Emphasis on disk subsystem
– Storage abstraction
– File system fundamentals
Parallel module
• Introduce threads as a
programming construct
• OS issues for supporting
parallel programming
• Architectural issues for
supporting parallel
programming
Network module
• Evolution of networking
hardware
• Network protocol stack
Connecting the different modules
• HLL constructs lead to
design of instruction-set for
LC-2200
• Processor implementation
of LC-2200
• Memory management
assists to LC-2200
• Interrupt and DMA support
to LC-2200
• ……
Why parallelism in a first course?
• Our motivation then (circa 98)
– Love affair of CS with parallelism
• PL and concurrency
• OS and concurrency
– Enablers in the 90’s
• Java, MT OS, multiple CPUs in
desktops
• In hindsight now
– Multicore CPUs
– Multithreading as a programming
concept in intro courses
Why networking in a first course?
• “box” without connectivity
is no good today
• Protocol stack is an integral
part of any OS
• Our motivation
– Understand evolution of
networking gear
– Understand mechanisms
needed in protocol stack
– Understand how a “box”
avails of network services
Where does this course fit?
• Assumed knowledge
– Logic design, assembly language,
and C programming
• New course is a first systems
course
– Preferably in sophomore year
• What follows?
– Advanced architecture, OS,
networking courses
– For those following other pursuits
• Sufficient exposure to “core”
Putting this pedagogical style in
practice
• 4 credit-hour semester
course or 5-credit hour
quarter course
• 45 hours of lecture
– Roughly 9 hours for each
module (some more than
others)
• 60-90 hours of unsupervised
lab time for projects
Experience at Georgia Tech
• CS 2200 introduced in Fall
1999
• Project component for
each module
– Concepts “get in” via
projects
– Collaboration allowed
• Key is “learning”
– Creativity in evaluation
Evaluating the pedagogy
• CS students hardware-averse
• OS and hardware together
makes “sense”
– Hardware design as an algorithmic
exercise
• Successful internships
– Anecdotal evidence from
industries and students
• Concepts learned early apply
to other domains (e.g. web
caching)
• Students better prepared for
advanced courses
• Informal poll
– At beginning of course
• 10% interested in the course
– At end of course
• Majority feel the course was useful
and important
• Increased interest in systems
– Number of UG students doing
research in systems
Other reasons why this is a good
approach
• Allows curricular innovation
• GT CS has been a leader
of innovation
– Evidence
• New ThreadsTM approach
• Chapter 7, Pages 309-315, “The
Right Stuff,” from THE WORLD IS
FLAT: UPDATED AND EXPANDED
EDITION, by Thomas L. Friedman
Meeting the Challenges
• Textbook
– Good books available for the
stovepipe model
– None for an integrated model
• We developed comprehensive
notes and slides
– Used standard textbooks as
background
• Responding to students
– Turned our courseware into online
textbook in 2005
• To match the style and content
• Available to the community
• In use for 8 consecutive semesters
(including summers)
Adopting the pedagogical style
• Online textbook
• Extensive online slides
• Several detailed project
ideas from 7+ years of
teaching this course
• Several problem sets and
model exams online
• In short
– Painless transition from
stovepipe model to this one
Comparison to other recent
pedagogical models
• Patt and Patel
– Logic design, assembly language,
plus C
– Ideal as a pre-req for our course
• Bryant and O’Hallaron
– Programmer’s perspective
– Goal
• How to create “power
programmers”?
• Important but different from our
focus
– Best applied to senior level UG
– A worthy follow on to our course
• Saltzer and Kaashoek
– System building blocks that
appear in different large
complex software systems
– Goal
• How to prepare students who
can create modular software
systems?
– A worthy follow on to our
course
Concluding remarks
• An integrated approach to
teaching computer system
architecture at sophomore
level
• Been in practice at GT for
7+ years
• Online textbook, slides,
project ideas, and tools
available for the whole
community
Applause!!!

Project: Processor Design
• Students given datapath
90% complete
• Project entails
– Completing the datapath
– Writing micro-code for
implementing LC-2200
instruction set
– Circuit design using
LogicWorks
Project: Interrupts and I/O
• Students supplied with LC-2200
simulator and LC-2200
assembler
• Project entails
– Adding circuitry to project 1 for
handling interrupts
– Enhancing the simulator to deal
with interrupts
– Writing an interrupt handler (in LC2200 assembly) to work with the
enhanced simulator
Project: Virtual memory subsystem
• Students supplied with a
processor plus memory
system simulator
• Project entails
– Developing a page-based
VM system on top
– Experimenting with different
page replacement
algorithms
Project: MT OS
• Students provided with a
processor plus memory system
simulator
• Project entails
– Implementing multithreaded OS
modules for managing the CPU
and I/O scheduling queues
– Parallel programming using
pthreads
– Experimenting with different CPU
scheduling algorithms
Project: Reliable Transport Layer
• Students provided with a
simulated network layer
• Project entails
– Implementing a reliable
transport that deals with
• Packet corruption
• Lost packets
• Out-of-order delivery of
packets
– Parallel programming using
pthreads