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Introduction to Computer Systems

Introduction to Computer Systems

Topics:Topics:Staff, text, and policiesLecture topics and assignmentsLab rationale

CS 213 F ’06

CS-213

Yan Chen

– 2 – CS-213, F’06

Teaching staffTeaching staffInstructor

Prof. Yan Chen (Thu 2-4pm, Tech L459)

TATBD

Undergraduate assistantResponsible for grading the homework and projects

Location and TimeLecture: 2-3:20pm, Tech M164

– 3 – CS-213, F’06

PrerequestsPrerequestsCS211 or equivalent RequiredExperience with C or C++ RequiredCS311 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 – CS-213, F’06

TextbooksTextbooksRequired:Required:

Randal E. Bryant and David R. Randal E. Bryant and David R. OO’’HallaronHallaron, , “Computer Systems: A Programmer’s Perspective”, Prentice Hall 2003.csapp.cs.cmu.edu

Recommended:Recommended:

Brian Kernighan and Dennis Ritchie, Brian Kernighan and Dennis Ritchie, “The C Programming Language, Second Edition”, Prentice Hall, 1988

Richard Stevens, Richard Stevens, “Advanced Programming in the Unix Environment”, Addison-Wesley, 1992

– 5 – CS-213, F’06

Homeworks, Labs, and ExamsHomeworks, Labs, and Exams3 labs, remove the malloc lab due to lack of TA3 ~ 4 homeworks, 2 exams

GradingGrading10% Homeworks10% Class attendance and discussion 30% Programming labs (10% per lab)25% Midterm (covers first half of the course)25% Final (covers second half of the course)

Late PolicyLate PolicyAfter 1 day, maximum score is 90%After 2 days, meximum score is 80%, etc.

– 6 – CS-213, F’06

Policies: AssignmentsPolicies: Assignments

Work groupsWork groupsYou must work in groups of 2 for all labs

HandinsHandinsAssignments due at 11:59pm on specified due date.Electronic handins only.

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Course ComponentsCourse ComponentsLecturesLectures

Higher level concepts

RecitationsRecitationsNone due to lack of TA

LabsLabsThe heart of the course2 ~ 3 weeksProvide in-depth understanding of an aspect of systemsProgramming and measurement

– 8 – CS-213, F’06

Getting HelpGetting HelpWebWeb

http://www.cs.northwestern.edu/~ychen/classes/cs213-f06/Copies of lectures, assignments, exams, solutions

NewsgroupNewsgroupcs.213For more info on newsgroup access, https://www.cs.northwestern.edu/support/services/news.php

Clarifications to assignments, general discussion

Personal helpPersonal helpProfessors: office hours 2-4pm on Thu.

– 9 – CS-213, F’06

CheatingCheatingWhat is cheating?What is cheating?

Sharing code: either by copying, retyping, looking at, or supplying a copy of a file.

What is NOT cheating?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:Penalty for cheating:Removal from course with failing grade.

– 10 – CS-213, F’06

Facilities Facilities TLAB (Tech FTLAB (Tech F--252: the Tech end of the bridge that 252: the Tech end of the bridge that

connects Tech and Ford) connects Tech and Ford) -- a cluster of Linux machines a cluster of Linux machines -- (e.g., TLAB(e.g., TLAB--11.cs.northwestern.edu) 11.cs.northwestern.edu)

You should all have TLAB accounts by now; You should all have TLAB accounts by now; --if not, contact root (if not, contact root (root@eecs.northwestern.eduroot@eecs.northwestern.edu))

For accessing the TLAB facilities For accessing the TLAB facilities -- contact Carol contact Carol SurmaSurma((carol@rhodes.ece.northwestern.educarol@rhodes.ece.northwestern.edu))

– 11 – CS-213, F’06

Programs and Data (8) Programs and Data (8)

TopicsTopicsBits operations, arithmetic, assembly language programs, representation of C control and data structuresIncludes aspects of architecture and compilers

AssignmentsAssignmentsL1: Manipulating bitsL2: Defusing a binary bombL3: Hacking a buffer bomb

– 12 – CS-213, F’06

The Memory Hierarchy (2)The Memory Hierarchy (2)

TopicsTopicsMemory technology, memory hierarchy, caches, disks, localityIncludes aspects of architecture and OS.

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Linking and Exceptional Control Flow (3)Linking and Exceptional Control Flow (3)

TopicsTopicsObject files, static and dynamic linking, libraries, loadingHardware exceptions, processes, process control, Unix signals, nonlocal jumpsIncludes aspects of compilers, OS, and architecture

– 14 – CS-213, F’06

Virtual Memory (2)Virtual Memory (2)

TopicsTopicsVirtual memory, address translation, dynamic storage allocationIncludes aspects of architecture and OS

– 15 – CS-213, F’06

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

TopicsTopicsHigh level and low-level I/O, network programming, Internet services, Web serversconcurrency, concurrent server design, threads, I/O multiplexing with select.Includes aspects of networking, OS, and architecture.

– 16 – CS-213, F’06

Lab Rationale Lab Rationale

Doing a lab should result in new skills and Doing a lab should result in new skills and conceptsconcepts

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.

– 17 – CS-213, F’06

Course ThemeCourse ThemeAbstraction is good, but don’t forget reality!

Courses to date emphasize abstractionCourses to date emphasize abstractionAbstract data typesAsymptotic analysis

These abstractions have limitsThese abstractions have limitsEspecially in the presence of bugsNeed to understand underlying implementations

Useful outcomesUseful outcomesBecome more effective programmers

Able to find and eliminate bugs efficientlyAble to tune program performance

Prepare for later “systems” classes in CS & ECECompilers, Operating Systems, Networks, Computer Architecture, Embedded Systems

– 18 – CS-213, F’06

Coarse GoalCoarse Goal

Must understand system to optimize Must understand system to optimize performanceperformance

How programs compiled and executedHow to measure program performance and identify bottlenecksHow to improve performance without destroying code modularity and generality

Implementations change, but concepts donImplementations change, but concepts don’’tt

– 19 – CS-213, F’06

Course PerspectiveCourse PerspectiveMost Systems Courses are BuilderMost Systems Courses are Builder--CentricCentric

Computer ArchitectureDesign pipelined processor in Verilog

Operating SystemsImplement large portions of operating system

CompilersWrite compiler for simple language

NetworkingImplement and simulate network protocols

– 20 – CS-213, F’06

Course Perspective (Cont.)Course Perspective (Cont.)Our Course is ProgrammerOur Course is Programmer--CentricCentric

Purpose is to show how by knowing more about the underlying system, one can be more effective as a programmerEnable you to

Write programs that are more reliable and efficientIncorporate features that require hooks into OS

» E.g., concurrency, signal handlers

Not just a course for dedicated hackersWe bring out the hidden hacker in everyone

Cover material in this course that you won’t see elsewhere

– 21 – CS-213, F’06

Hello WorldHello WorldWhat happens and why when you run What happens and why when you run ““hellohello””

on your system?on your system?

Goal: introduce key concepts, terminology, and Goal: introduce key concepts, terminology, and componentscomponents

/*hello world*/# include <stdio.h>

int main(){

printf(“hello, world\n”);}

/*hello world*/# include <stdio.h>

int main(){

printf(“hello, world\n”);}

– 22 – CS-213, F’06

Information is Bits + ContextInformation is Bits + Context““HelloHello”” is a source codeis a source code

Sequence of bits (0 or 1)8-bit data chunks are called BytesEach Byte has an integer value that corresponds to some character (ASCII standard)

E.g., ‘#’ -> 35

Files that consist of ASCII characters -> text filesAll other files -> binary files (e.g., 35 is a part of a machine command)

Context is importantContext is importantThe same sequence of bytes might represent a character string or machine instruction

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Programs Translated by Other ProgramsPrograms Translated by Other Programs

Pre-processor

(cpp)

hello.i Compiler(cc1)

hello.s Assembler(as)

hello.o Linker(ld)

hellohello.c

Sourceprogram

(text)

Modifiedsource

program(text)

Assemblyprogram

(text)

Relocatableobject

programs(binary)

Executableobject

program(binary)

printf.o

Pre-processingE.g., #include <stdio.h> is inserted into hello.i

Compilationhello.s: each statement is an assembly language program

Assemblyhello.o: 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

unix> gcc –o hello hello.cunix> gcc –o hello hello.c

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Why do We Care about This?Why do We Care about This?Optimizing program performanceOptimizing program performance

To write efficient code

Understanding linkUnderstanding link--time errorstime errorsWhy does it matter what order we list libraries?Why some link-errors do not appear before run time?

Avoiding security holesAvoiding security holesBuffer overflow bugs

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ShellShell

ShellShell

a commanda command--line interpreter thatline interpreter that

prints a promptprints a prompt

waits for you to type command linewaits for you to type command line

loads and runs hello programloads and runs hello program

prints a promptprints a prompt

unix> ./hellohello, worldunix>

unix> ./hellohello, worldunix>

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Hardware organizationHardware organization BusesBusesTransfer fixed-sized chunks of data (WORDS)Intel Pentium -> 4Bytes bus

Mainmemory

I/O bridgeBus interface

ALU

Register file

CPU

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard DisplayDisk

I/O bus Expansion slots forother devices suchas network adapters

hello executable stored on disk

PC

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Hardware organizationHardware organization I/O DevicesI/O DevicesSystem connections to external worldMouse, keyboard (input)Display, disk device (output)

Mainmemory

I/O bridgeBus interface

ALU

Register file

CPU

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard DisplayDisk

I/O bus Expansion slots forother devices suchas network adapters

hello executable stored on disk

PC

– 28 – CS-213, F’06

Hardware organizationHardware organizationMain MemoryMain Memory

Temporary storage deviceHolds both a program and the data it manipulates with

Mainmemory

I/O bridgeBus interface

ALU

Register file

CPU

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard DisplayDisk

I/O bus Expansion slots forother devices suchas network adapters

hello executable stored on disk

PC

– 29 – CS-213, F’06

Hardware organizationHardware organization

Control Processor Unit Control Processor Unit (CPU)(CPU)

Executes instructions stored in main memoryProgram Counter (PC or Register) contains the address of some machine-language instruction from memory

Mainmemory

I/O bridgeBus interface

ALU

Register file

CPU

System bus Memory bus

PC

CPUCPUReads the instruction from memoryPerforms simple operation (load, store, update)Updates the PC to point to next instruction

– 30 – CS-213, F’06

Running the Hello ProgramRunning the Hello ProgramReading the hello command from the keyboardReading the hello command from the keyboard

Mainmemory

I/O bridgeBus interface

ALU

Register file

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard DisplayDisk

I/O bus Expansion slots forother devices suchas network adapters

PC

"hello"

User types "hello"

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Running the Hello ProgramRunning the Hello ProgramShell program loads Shell program loads hello.exehello.exe into main memoryinto main memory

Mainmemory

I/O bridgeBus interface

ALU

Register file

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard DisplayDisk

I/O bus Expansion slots forother devices suchas network adapters

hello executable stored on disk

PC

hello code

"hello,world\n"

– 32 – CS-213, F’06

Running the Hello ProgramRunning the Hello ProgramThe processor executes instructions and displays The processor executes instructions and displays ““hellohello…”…”

Mainmemory

I/O bridgeBus interface

ALU

Register file

System bus Memory bus

Disk controller

Graphicsadapter

USBcontroller

Mouse Keyboard DisplayDisk

I/O bus Expansion slots forother devices suchas network adapters

hello executable stored on disk

PC

hello code

"hello,world\n"

"hello,world\n"

– 33 – CS-213, F’06

CachingCachingA system spends a lot of time moving information from one place to anotherLarger storage devices are slower than smaller ones

Register file ~ 100 BytesMain memory ~ millions of Bytes

It is easier and cheaper to make processors run faster than it is to make main memory run faster

Mainmemory(DRAM)

MemorybridgeBus interfaceL2 cache

(SRAM)

ALU

Register fileCPU chip

Cache bus System bus Memory bus

L1 cache

(SRAM)

– 34 – CS-213, F’06

Storage Devices Form a HierarchyStorage Devices Form a HierarchyStorage at one level serves as cache at the next Storage at one level serves as cache at the next

levellevelRegisters

On-chip L1cache (SRAM)

Main memory(DRAM)

Local secondary storage(local disks)

Larger, slower,

and cheaper (per byte)storagedevices

Remote secondary storage(distributed file systems, Web servers)

Local disks hold files retrieved from disks on remote network servers.

Main memory holds disk blocks retrieved from local disks.

Off-chip L2cache (SRAM)

L1 cache holds cache lines retrieved from the L2 cache.

CPU registers hold words retrieved from cache memory.

L2 cache holds cache lines retrieved from memory.

L0:

L1:

L2:

L3:

L4:

L5:

Smaller,faster,and

costlier(per byte)storage devices

– 35 – CS-213, F’06

Operating System (OS)Operating System (OS)OS OS –– a layer of software interposed between the a layer of software interposed between the

application program and the hardwareapplication program and the hardware

Two primary purposesTwo primary purposesTo protect the hardware from misuse by applicationsTo provide simple and uniform mechanisms for manipulating low-level hardware devices

Application programs

Processor Main memory I/O devices

Operating systemSoftware

Hardware

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OS AbstractionsOS AbstractionsFiles are abstractions of I/O devicesFiles are abstractions of I/O devices

Virtual Memory is an abstraction for the main Virtual Memory is an abstraction for the main memory and I/O devicesmemory and I/O devices

Processes are abstractions for the processor, Processes are abstractions for the processor, main memory, and I/O devicesmain memory, and I/O devices

Processor Main memory I/O devices

Processes

Files

Virtual memory

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ProcessesProcessesThe OS provides the illusion that the program is The OS provides the illusion that the program is

the only one in the systemthe only one in the system

Process Process OS’s abstraction of a running program

Context switchingContext switchingSaving the context of one processRestoring the process of the new process

shell process

helloprocess

Application code

Time

Context switch

Context switch

OS code

Application code

OS code

Application code

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Virtual MemoryVirtual MemoryIllusion that Illusion that each each process has process has exclusive exclusive use of main use of main memorymemory

ExampleExampleThe virtual address space for Linux

Kernel virtual memory

Memory mapped region forshared libraries

Run-time heap(created at runtime by malloc)

User stack(created at runtime)

Unused0

Memoryinvisible touser code0xc0000000

0x08048000

0x40000000

Read/write data

Read-only code and data

Loaded from the hello executable file

printf() function

0xffffffff

– 39 – CS-213, F’06

NetworkingNetworkingComputers do more than execute programsComputers do more than execute programs

They need to get data in and outThey need to get data in and outI/O system critical to program reliability and performance

They communicate with each other over They communicate with each other over networksnetworks

Many system-level issues arise in presence of network

Coping with unreliable mediaCross platform compatibilityComplex performance issues