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Introduction to Computer Systems
Today:
Welcome to EECS 213
Lecture topics and assignments
Lab rationale
Next time:
Bits & bytes
and some Boolean algebra
Fabián E. Bustamante, Spring 2007
Welcome to Intro. to Computer Systems
Everything you need to know
http://www.cs.northwestern.edu/~fabianb/classes/eecs-213.html
Your instructor: Fabián E. Bustamante
Your TA: we’ll see about that
Your undergraduate assistant
– Helping with grading homework and projects
Communication channels:
– Course webpage
– News
– eecs-213@cs
EECS 213 Introduction to Computer Systems
Northwestern University
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Course theme
Abstraction is good, but don’t forget reality!
Courses to date emphasize abstraction
– Abstract data types, asymptotic analysis, …
Abstractions have limits
– Especially in the presence of bugs
– Need to understand underlying implementations
Useful outcomes
– Become more effective programmers
• Better at debugging, performance tuning, …
– Prepare for later “systems” classes in CS & ECE
• Compilers, Operating Systems, Networks, ...
– What do you need?
• Required: EECS 211 or equivalent & Experience with C or C++
• Useful: EECS 311
EECS 213 Introduction to Computer Systems
Northwestern University
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Course perspective
Most systems courses are builder-centric
– Operating Systems: Implement portions of an OS
– Compilers: Write compiler for simple language
– Networking: Implement and simulate network protocols
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
– Not just a course for dedicated hackers
• We bring out the hidden hacker in everyone
– Cover material in this course that you won’t see elsewhere
EECS 213 Introduction to Computer Systems
Northwestern University
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Textbooks
Required:
– Bryant & O’Hallaron, “Computer Systems: A
Programmer’s Perspective”, PH 2003.
(csapp.cs.cmu.edu)
Recommended:
– Kernighan & Ritchie (K&R), “The C Programming
Language, Second Edition”, PH 1988
– R. Stevens, “Advanced Programming in the Unix
Environment”, AW 1992; there’s a new edition by R.
Stevens and S. Rago, AW 2005
EECS 213 Introduction to Computer Systems
Northwestern University
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Course components
Lectures
– Higher level concepts
– 10% of grade from class participation
Labs
– The heart of the course – in-depth understanding
– 3 labs, remove the malloc lab due to lack of TA
• 2 ~ 3 weeks
– 10% of grade each
– Working on teams of 2
Homework assignments (3-4)
– 10% of grade
Exams – midterm & final
– 25% of grade each
EECS 213 Introduction to Computer Systems
Northwestern University
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Policies
Late policy
– 10% off per day
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.
EECS 213 Introduction to Computer Systems
Northwestern University
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Facilities
TLAB (Tech F-252, on the bridge to Ford)
– A cluster of Linux machines (e.g., TLAB11.cs.northwestern.edu)
You should all have TLAB accounts by now;
problems? contact root
([email protected])
Need physical access to TLAB? Contact Carol
Surma ([email protected])
EECS 213 Introduction to Computer Systems
Northwestern University
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Lab rationale
Doing a lab should result in new skills and
concepts
– Data Lab: computer arithmetic, digital logic.
– Bomb Lab: assembly language, using a debugger,
understanding the stack.
– Exploit Lab: understanding the calling stack
organization and buffer overflow vulnerabilities.
EECS 213 Introduction to Computer Systems
Northwestern University
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Some topics covered
Programs and data
– Bits arithmetic, assembly, representation of C control …
– Includes aspects of architecture and compilers
Memory hierarch
– Memory technology, memory hierarchy, caches, disks, locality
– Includes aspects of architecture and OS.
Linking & exceptional control flow
– Object files, dynamic linking, libraries, process control, …
– Includes aspects of compilers, OS, and architecture
Virtual memory
– Virtual memory, address translation, dynamic storage
allocation
– Includes aspects of architecture and OS
I/O, networking & concurrency
– High level & low-level I/O, net programming, threads, …
– Includes aspects of networking, OS, and architecture
EECS 213 Introduction to Computer Systems
Northwestern University
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Hello World
What happens and why when you run “hello”
on your system?
/*hello world*/
# include <stdio.h>
int main()
{
printf(“hello, world\n”);
}
Goal: introduce key concepts, terminology,
and components
EECS 213 Introduction to Computer Systems
Northwestern University
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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., ‘#’ -> 35
– Files that consist of ASCII characters -> text files
– All other files -> 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
EECS 213 Introduction to Computer Systems
Northwestern University
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Programs translated by other programs
unix> gcc –o hello hello.c
printf.o
hello.c
Source
program
(text)
Prehello.i
processor
(cpp)
Modified
source
program
(text)
Compiler hello.s
(cc1)
Assembly
program
(text)
Assembler hello.o
(as)
Linker
(ld)
Relocatable
object
programs
(binary)
hello
Executable
object
program
(binary)
Pre-processing
– E.g., #include <stdio.h> is inserted into hello.i
Compilation (.s)
– Each statement is an assembly language program
Assembly (.o)
– A binary file whose bytes encode mach. language instructions
Linking
– Get printf() which resides in a separate precompiled object file
EECS 213 Introduction to Computer Systems
Northwestern University
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Hardware organization
CPU
Buses: transfer fixed-sized
chunks of data (WORDS)
Pentium: 4B bus
Register file
PC
ALU
Bus interface
I/O Devices: System connections
to external world.
Mouse, keyboard (input);
Display, disk device (output)
System bus
Memory bus
Control Processor Unit
Executes instructions stored
inI/O
MM. PC - holds addressMain
memory
bridge
of machine-language
instruction from memory
I/O bus
USB
controller
Mouse Keyboard
Graphics
adapter
Main Memory: Temporary
storage Expansion
device. Holds
both
slots
for a
programother
and the
data such
it
devices
manipulates.
as network adapters
Disk
controller
Display
Disk
EECS 213 Introduction to Computer Systems
Northwestern University
hello executable
stored on disk
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Running Hello
Running hello
unix> ./hello
hello, world
unix>
What’s the shell?
What does it do?
– prints a prompt
– waits for you to type command line
– loads and runs hello program …
EECS 213 Introduction to Computer Systems
Northwestern University
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Running Hello
Reading the hello command
from the keyboard
Register file
PC
ALU
System bus
Memory bus
Main “./hello"
memory
I/O
bridge
Bus interface
I/O bus
USB
controller
Mouse Keyboard
Graphics
adapter
Disk
controller
Expansion slots for
other devices such
as network adapters
Display
Disk
User types "hello"
EECS 213 Introduction to Computer Systems
Northwestern University
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Running Hello
Shell program loads hello.exe
into main memory
Register file
PC
ALU
"hello,world\n"
System bus
Memory bus
Main
memory
I/O
bridge
Bus interface
hello code
I/O bus
USB
controller
Mouse Keyboard
Graphics
adapter
Disk
controller
Display
Disk
EECS 213 Introduction to Computer Systems
Northwestern University
Expansion slots for
other devices such
as network adapters
hello executable
stored on disk
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Running Hello
The processor executes instructions
and displays “hello…”
Register file
PC
ALU
"hello,world\n"
System bus
Memory bus
Main
memory
I/O
bridge
Bus interface
hello code
I/O bus
USB
controller
Mouse Keyboard
Graphics
adapter
Disk
controller
Display
"hello,world\n"
Disk
EECS 213 Introduction to Computer Systems
Northwestern University
Expansion slots for
other devices such
as network adapters
hello executable
stored on disk
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Caches matter
System spends a lot of time moving info. around
Larger storage devices are slower than smaller ones
– Register file ~ 100 Bytes & Main memory ~ millions of Bytes
Easier and cheaper to make processors run faster
than to make main memory run faster
– Standard answer – cache
CPU chip
Register file
L1
cache
ALU
(SRAM)
Cache bus
L2 cache
(SRAM)
System bus
Bus interface
Memory
bridge
EECS 213 Introduction to Computer Systems
Northwestern University
Memory bus
Main
memory
(DRAM)
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Storage devices form a hierarchy
L0:
Registers
Storage at one level
serves as cache at
the next level
L1:
L2:
Smaller,
faster,
and
costlier
(per byte)
storage
devices
L3:
L4:
L5:
CPU registers hold words retrieved from
cache memory.
On-chip L1
cache (SRAM)
L1 cache holds cache lines retrieved
from the L2 cache.
Off-chip L2
cache (SRAM)
L2 cache holds cache lines
retrieved from memory.
Main memory
(DRAM)
Local secondary storage
(local disks)
Main memory holds disk
blocks retrieved from local
disks.
Local disks hold files
retrieved from disks on
remote network servers.
Remote secondary storage
(distributed file systems, Web servers)
EECS 213 Introduction to Computer Systems
Northwestern University
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Operating System
OS – a layer of software interposed between
the application program and the hardware
Application programs
Software
Operating system
Processor
Main memory
I/O devices
Hardware
Two primary goal
– Protect resources from misuse by applications
– Provide simple and uniform mechanisms for
manipulating low-level hardware devices
EECS 213 Introduction to Computer Systems
Northwestern University
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OS Abstractions
Files – abstractions of I/O devices
Virtual Memory – abstraction for main memory
and I/O devices
Processes – abstractions for processor, main
memory, and I/O devices
Processes
Virtual memory
Files
Processor
Main memory
I/O devices
EECS 213 Introduction to Computer Systems
Northwestern University
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Processes
OS provides the illusion that a process is the only one
there
Process
– OS’s abstraction of a running program
Context switch
– Saving context of one process, restoring that of another one
– Distorted notion of time
Time
shell
process
hello
process
Application code
OS code
Context
switch
Application code
OS code
Context
switch
Application code
EECS 213 Introduction to Computer Systems
Northwestern University
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Virtual Memory
Illusion that each
process has
exclusive use of
a large main
memory
Example
– Virtual address
space for Linux
0xffffffff
0xc0000000
Kernel virtual memory
Memory
invisible to
user code
User stack
(created at runtime)
0x40000000
Memory mapped region for
shared libraries
printf()
function
Run-time heap
(created at runtime by malloc)
Read/write data
Read-only code and data
Loaded from
the hello
executable file
0x08048000
0
Unused
EECS 213 Introduction to Computer Systems
Northwestern University
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Networking
Talking to other systems
Network – seen as another I/O device
Many system-level issues arise in presence of network
– Coping with unreliable media
– Cross platform compatibility
– Complex performance issues
Expansion slots
I/O bus
USB
controller
Mouse Keyboard
Graphics
adapter
Disk
controller
Display
Disk
EECS 213 Introduction to Computer Systems
Northwestern University
Network
adapter
Network
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Conclusions
Any computer system is more than just
hardware
– A collection of intertwined hardware & software that
must cooperate to achieve the end goal – running
applications
The rest of our course will expand on this
EECS 213 Introduction to Computer Systems
Northwestern University
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