Introduction to Computer Systems

1
Introduction to Computer Systems
CS-213
Aleksandar Kuzmanovic 3/27/2006

• Topics
• Staff, text, and policies
• Lecture topics and assignments
• Class overview

CS 213 S 06
2
Teaching staff

• Instructor
• Prof. Aleksandar Kuzmanovic (Wed 1000-1200,
  Tech L457)
• TA
• David Choffnes (Tu, Th 1-230, Ford 2-217)
• Recitation (Tu, 5-630, Tech MG28)
• Undergraduate assistant
• TBA (TBA)
• Location and Time
• Lecture MW 2-320, Tech LR3
• Recitation Tu, 5-630, Tech MG28

3
Prerequests

• CS211 (Fund. of comp. program.) or eq. Required
• Experience with C or C Required
• CS311 (Data structures and mgmt) Useful
• CS213 is required CS course
• It is prerequisite for CS 343 (Operating Systems)
• It is also prerequisite for ALL systems courses
• See http//nsrg.cs.northwestern.edu for a current
  list

4
Textbooks

• Required
• Randal E. Bryant and David R. OHallaron,
• Computer Systems A Programmers Perspective,
  Prentice Hall 2003.
• csapp.cs.cmu.edu
• Recommended
• Brian Kernighan and Dennis Ritchie,
• The C Programming Language, Second Edition,
  Prentice Hall, 1988
• Richard Stevens,
• Advanced Programming in the Unix Environment,
  Addison-Wesley, 1992

5
Homeworks, Labs, and Exams

• 4 labs, 4 homeworks, 2 exams
• Grading
• 10 Homeworks (2.5 per homework)
• 50 Programming labs (12.5 per lab)
• 20 Midterm (covers first half of the course)
• 20 Final (covers second half of the course)
• Final grades gt90 (or 90th percentile) A
• gt80 (or 80th percentile)
  B,
• gt70 (or 70th percentile)
  C, etc.
• Late Policy
• After 1 day, maximum score is 90
• After 2 days, maximum score is 80, etc.

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Policies Assignments

• Work groups
• You must work in groups of 2 for all labs
• Let me and the TA know the groups by the end of
  the week
• Handins
• Assignments due at 1159pm on specified due date.
• Electronic handins only.

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Course Components

• Lectures
• Higher level concepts
• Recitations
• Applied concepts, important tools and skills for
  labs, clarification of lectures, exam coverage
• Labs
• The heart of the course
• 1 or 2 weeks
• Provide in-depth understanding of an aspect of
  systems
• Programming and measurement

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Getting Help

• Web
• http//cs.northwestern.edu/akuzma/classes/CS213-s
  06/
• Copies of lectures, assignments, handouts
• Clarifications to assignments
• Newsgroups
• cs.213.announce and
• cs.213.discuss
• Clarifications to assignments, general discussion
  
• Cant reply immediately!
• Personal help
• Professor, Wednesdays 10-noon
• TA Tu, Th 1-230

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Cheating

• What is cheating?
• Sharing code either by copying, retyping,
  looking at, or supplying a copy of a file.
• What is NOT cheating?
• Helping others use systems or tools.
• Helping others with high-level design issues.
• Helping others debug their code.
• Penalty for cheating
• Removal from course with failing grade.

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Facilities

• TLAB (Tech F-252 the Tech end of the bridge that
  connects Tech and Ford)
• - a cluster of Linux machines
• - (e.g., TLAB-11.cs.northwestern.edu)
• You should all have TLAB accounts by now
• -if not, contact Scott Hoover (scott_at_cs.northwest
  ern.edu)
• For accessing the TLAB facilities
• - contact Carol Surma (carol_at_rhodes.ece.northwest
  ern.edu)
• Should you have other problems
• - contact the TA directly

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Programs and Data (8)

• Topics
• Bits operations, arithmetic, assembly language
  programs, representation of C control and data
  structures
• Includes aspects of architecture and compilers
• Assignments
• L1 Manipulating bits
• L2 Defusing a binary bomb
• L3 Hacking a buffer bomb

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The Memory Hierarchy (2)

• Topics
• Memory technology, memory hierarchy, caches,
  disks, locality
• Includes aspects of architecture and OS.

13
Linking and Exceptional Control Flow (3)

• Topics
• Object files, static and dynamic linking,
  libraries, loading
• Hardware exceptions, processes, process control,
  Unix signals, nonlocal jumps
• Includes aspects of compilers, OS, and
  architecture

14
Virtual memory (2)

• Topics
• Virtual memory, address translation, dynamic
  storage allocation
• Includes aspects of architecture and OS
• Assignments
• L4 Writing your own malloc package

15
I/O, Networking, and Concurrency (3)

• Topics
• High level and low-level I/O, network
  programming, Internet services, Web servers
• concurrency, concurrent server design, threads,
  I/O multiplexing with select.
• Includes aspects of networking, OS, and
  architecture.

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Lab Rationale

• Doing a lab should result in new skills and
  concepts
• Data Lab computer arithmetic, digital logic.
• Bomb Labs assembly language, using a debugger,
  understanding the stack
• Malloc Lab understanding pointers and nasty
  memory bugs.

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Course Theme

• Abstraction is good, but dont forget reality!
• Courses to date emphasize abstraction
• Abstract data types
• Asymptotic analysis
• These abstractions have limits
• Especially in the presence of bugs
• Need to understand underlying implementations
• Useful outcomes
• Become more effective programmers
• Able to find and eliminate bugs efficiently
• Able to tune program performance
• Prepare for later systems classes in CS ECE
• Compilers, Operating Systems, Networks, Computer
  Architecture, Embedded Systems

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Coarse Goal

• Must understand system to optimize performance
• How programs compiled and executed
• How to measure program performance and identify
  bottlenecks
• How to improve performance without destroying
  code modularity and generality
• Implementations change, but concepts dont

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Course Perspective

• Most Systems Courses are Builder-Centric
• Computer Architecture
• Design a processor
• Operating Systems
• Implement large portions of operating system
• Compilers
• Write compiler for simple language
• Networking
• Implement and simulate network protocols

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Course Perspective (Cont.)

• This Course is Programmer-Centric
• Purpose is to show how by knowing more about the
  underlying system, one can be more effective as a
  programmer
• Enable you to
• Write programs that are more reliable and
  efficient
• Incorporate features that require hooks into OS
• E.g., concurrency, signal handlers
• Cover material in this course that you wont see
  elsewhere

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Hello World

• In a sense, the goal of the course is to help you
  understand what happens and why when you run
  hello on your system?
• Goal introduce key concepts, terminology, and
  components

/hello world/ include ltstdio.hgt int
main() printf(hello, world\n)
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Information is Bits Context

• Hello is a source code
• Sequence of bits (0 or 1)
• 8-bit data chunks are called Bytes
• Each Byte has an integer value that corresponds
  to some character (ASCII standard)
• E.g., -gt 35
• Files that consist of ASCII characters -gt text
  files
• All other files -gt binary files (e.g., 35 is a
  part of a machine command)
• Context is important
• The same sequence of bytes might represent a
  character string or machine instruction
• Machines put everything in bits!
• Chapter 2 -gt machine representations of numbers

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Programs Translated by Other Programs
unixgt gcc o hello hello.c

• Phases
• Pre-processing
• E.g., include ltstdio.hgt is inserted into hello.i
• Compilation
• hello.s -gt each statement is an assembly language
  program
• Assembly
• hello.o -gt is a binary file whose bytes encode
  machine language instructions
• Linking
• E.g., hello.c uses printf(), it resides in a
  separate precompiled object file printf.o

printf.o
Pre- processor (cpp)
Compiler (cc1)
Assembler (as)
Linker (ld)
hello.i
hello.s
hello.o
hello
hello.c
Source program (text)
Assembly program (text)
Modified source program (text)
Relocatable object programs (binary)
Executable object program (binary)
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Why do We Care about This?

• Optimizing program performance
• To write efficient code -gt we do need a basic
  understanding of how a compiler translates
  different C statements into assembly language
• How to tune C programs to help compiler
• Understanding link-time errors
• Why does it matter what order we list libraries?
• Why some link-errors do not appear before run
  time?
• Avoiding security holes
• Buffer overflow bugs

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Shell

• Shell
• a command-line interpreter that
• - prints a prompt
• - waits for you to type command line
• - loads and runs hello program
• - prints a prompt

unixgt ./hello hello, world unixgt
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Hardware organization

• Buses
• Transfer fixed-sized chunks of data (WORDS)
• Intel Pentium -gt 4Bytes bus

CPU
Register file
ALU
PC
System bus
Memory bus
Main memory
I/O bridge
Bus interface
I/O bus
Expansion slots for other devices such as network
adapters
USB controller
Disk controller
Graphics adapter
Mouse
Keyboard
Display
Disk
hello executable stored on disk
27
Hardware organization

• I/O Devices
• System connections to external world
• Mouse, keyboard (input)
• Display, disk device (output)

CPU
Register file
ALU
PC
System bus
Memory bus
Main memory
I/O bridge
Bus interface
I/O bus
Expansion slots for other devices such as network
adapters
USB controller
Disk controller
Graphics adapter
Mouse
Keyboard
Display
Disk
hello executable stored on disk
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Hardware organization

• Main Memory
• Temporary storage device
• Holds both a program and the data it manipulates
  with

CPU
Register file
ALU
PC
System bus
Memory bus
Main memory
I/O bridge
Bus interface
I/O bus
Expansion slots for other devices such as network
adapters
USB controller
Disk controller
Graphics adapter
Mouse
Keyboard
Display
Disk
hello executable stored on disk
29
Hardware organization
CPU
Register file
ALU
PC
System bus
Memory bus
Main memory
I/O bridge
Bus interface

• CPU
• Reads the instruction from memory
• Performs simple operation (load, store, update)
• Updates the PC to point to next instruction

• Control Processor Unit (CPU)
• Executes instructions stored in main memory
• Program Counter (PC or Register) contains the
  address of some machine-language instruction from
  memory

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Running the Hello Program

• Reading the hello command from the keyboard

Register file
ALU
PC
System bus
Memory bus
Main memory
"hello"
I/O bridge
Bus interface
I/O bus
Expansion slots for other devices such as network
adapters
USB controller
Disk controller
Graphics adapter
Mouse
Keyboard
Display
Disk
User types "hello"
31
Running the Hello Program

• Shell program loads hello.exe into main memory

Register file
ALU
PC
System bus
Memory bus
Main memory
"hello,world\n"
I/O bridge
Bus interface
hello code
I/O bus
Expansion slots for other devices such as network
adapters
USB controller
Disk controller
Graphics adapter
Mouse
Keyboard
Display
Disk
hello executable stored on disk
32
Running the Hello Program

• The processor executes instructions and displays
  hello

Register file
ALU
PC
System bus
Memory bus
Main memory
"hello,world\n"
I/O bridge
Bus interface
hello code
I/O bus
Expansion slots for other devices such as network
adapters
USB controller
Disk controller
Graphics adapter
Mouse
Keyboard
Display
Disk
hello executable stored on disk
"hello,world\n"
33
Caching

• A system spends a lot of time moving information
  from one place to another
• Larger storage devices are slower than smaller
  ones
• Register file 100 Bytes
• Main memory millions of Bytes
• It is easier and cheaper to make processors run
  faster than it is to make main memory run faster
  (SRAM Static RAM)

CPU chip
Register file
L1 cache (SRAM)
ALU
Cache bus
System bus
Memory bus
Main memory (DRAM)
Memory bridge
Bus interface
L2 cache (SRAM)
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Storage Devices Form a Hierarchy

• Storage at one level serves as cache at the next
  level

L0
Smaller, faster, and costlier (per byte) storage
devices
Registers
CPU registers hold words retrieved from cache
memory.
On-chip L1 cache (SRAM)
L1
Off-chip L2 cache (SRAM)
L2
Main memory (DRAM)
L3
Larger, slower, and cheaper (per
byte) storage devices
Local secondary storage (local disks)
L4
Remote secondary storage (distributed file
systems, Web servers)
L5
35
Operating System (OS)

• OS a layer of software interposed between the
  application program and the hardware
• Two primary purposes
• To protect the hardware from misuse by
  applications
• To provide simple and uniform mechanisms for
  manipulating low-level hardware devices

Application programs
Software
Operating system
Processor
Main memory
I/O devices
Hardware
36
OS Abstractions

• Files are abstractions of I/O devices
• Virtual Memory is an abstraction for the main
  memory and I/O devices
• Processes are abstractions for the processor,
  main memory, and I/O devices

Processes
Virtual memory
Files
Processor
Main memory
I/O devices
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Processes

• The OS provides the illusion that the program is
  the only one in the system
• Process
• OSs abstraction of a running program
• Context switching
• Saving the context of one process
• Restoring the process of the new process

shell process
hello process
Time
Application code
Context switch
OS code
Application code
Context switch
OS code
Application code
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Virtual Memory
Memory invisible to user code
0xffffffff

• Illusion that each process has exclusive use of
  main memory
• Example
• The virtual address space for Linux

Kernel virtual memory
0xc0000000
User stack (created at runtime)
Memory mapped region for shared libraries
printf() function
0x40000000
Run-time heap (created at runtime by malloc)
Read/write data
Loaded from the hello executable file
Read-only code and data
0x08048000
Unused
0
39
Networking

• Computers do more than execute programs
• They need to get data in and out
• I/O system critical to program reliability and
  performance
• They communicate with each other over networks
• Because of the Internet, copying info from 1
  machine to another has become important