Introduction to Computer Systems

1. 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

2. 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 SystemsNorthwestern University

3. 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 SystemsNorthwestern University

4. 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 SystemsNorthwestern University

5. 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 SystemsNorthwestern University

6. 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 SystemsNorthwestern University

7. 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 SystemsNorthwestern University

8. Facilities • TLAB (Tech F-252, on the bridge to Ford) • A cluster of Linux machines (e.g., TLAB-11.cs.northwestern.edu) • You should all have TLAB accounts by now; problems? contact root (root@eecs.northwestern.edu) • Need physical access to TLAB? Contact Carol Surma (carol@rhodes.ece.northwestern.edu) EECS 213 Introduction to Computer SystemsNorthwestern University

9. 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 SystemsNorthwestern University

10. 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 SystemsNorthwestern University

11. Hello World • What happens and why when you run “hello” on your system? • Goal: introduce key concepts, terminology, and components /*hello world*/ # include <stdio.h> int main() { printf(“hello, world\n”); } EECS 213 Introduction to Computer SystemsNorthwestern University

12. 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 SystemsNorthwestern University

13. Programs translated by other programs unix> gcc –o hello hello.c • 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 printf.o Pre- processor (cpp) Compiler (cc1) Assembler (as) Linker (ld) hello.c hello.i hello.s hello.o hello Source program (text) Assembly program (text) Modified source program (text) Relocatable object programs (binary) Executable object program (binary) EECS 213 Introduction to Computer SystemsNorthwestern University

14. CPU Register file ALU PC System bus Memory bus Main memory Bus interface I/O bridge I/O bus Expansion slots for other devices such as network adapters USB controller Graphics adapter Disk controller Mouse Keyboard Display Disk hello executable stored on disk Hardware organization • Buses: transfer fixed-sized chunks of data (WORDS) • Pentium: 4B bus • Control Processor Unit • Executes instructions stored in MM. PC - holds address of machine-language instruction from memory • I/O Devices: System connections to external world. • Mouse, keyboard (input); Display, disk device (output) Main Memory: Temporary storage device. Holds both a program and the data it manipulates. EECS 213 Introduction to Computer SystemsNorthwestern University

15. Running Hello • Running hello • What’s the shell? • What does it do? • prints a prompt • waits for you to type command line • loads and runs hello program … unix> ./hello hello, world unix> EECS 213 Introduction to Computer SystemsNorthwestern University

16. Register file ALU PC System bus Memory bus Main memory “./hello" Bus interface I/O bridge I/O bus Expansion slots for other devices such as network adapters USB controller Graphics adapter Disk controller Mouse Keyboard Display Disk User types "hello" Running Hello Reading the hello command from the keyboard EECS 213 Introduction to Computer SystemsNorthwestern University

17. Register file ALU PC "hello,world\n" System bus Memory bus Main memory Bus interface I/O bridge hello code I/O bus Expansion slots for other devices such as network adapters USB controller Graphics adapter Disk controller Mouse Keyboard Display Disk hello executable stored on disk Running Hello Shell program loads hello.exe into main memory EECS 213 Introduction to Computer SystemsNorthwestern University

18. Register file ALU PC "hello,world\n" System bus Memory bus Main memory Bus interface I/O bridge hello code I/O bus Expansion slots for other devices such as network adapters USB controller Graphics adapter Disk controller Mouse Keyboard Display Disk hello executable stored on disk "hello,world\n" Running Hello The processor executes instructions and displays “hello…” EECS 213 Introduction to Computer SystemsNorthwestern University

19. CPU chip Register file L1 cache (SRAM) ALU Cache bus System bus Memory bus Main memory (DRAM) L2 cache (SRAM) Bus interface Memory bridge 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 EECS 213 Introduction to Computer SystemsNorthwestern University

20. L1 cache holds cache lines retrieved from the L2 cache. L2 cache holds cache lines retrieved from memory. Main memory holds disk blocks retrieved from local disks. Local disks hold files retrieved from disks on remote network servers. Storage devices form a hierarchy L0: CPU registers hold words retrieved from cache memory. Storage at one level serves as cache at the next level Registers On-chip L1 cache (SRAM) L1: Off-chip L2 cache (SRAM) L2: Smaller, faster, and costlier (per byte) storage devices Main memory (DRAM) L3: Local secondary storage (local disks) L4: Remote secondary storage (distributed file systems, Web servers) L5: EECS 213 Introduction to Computer SystemsNorthwestern University

21. Application programs Software Operating system Processor Main memory I/O devices Hardware Operating System • OS – a layer of software interposed between the application program and the 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 SystemsNorthwestern University

22. Processes Virtual memory Files Processor Main memory I/O devices 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 EECS 213 Introduction to Computer SystemsNorthwestern University

23. shell process hello process Time Application code Context switch OS code Application code Context switch OS code Application code 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 EECS 213 Introduction to Computer SystemsNorthwestern University

24. 0xffffffff Memory invisible to user code 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 helloexecutable file Read-only code and data 0x08048000 Unused 0 Virtual Memory • Illusion that each process has exclusive use of a large main memory • Example • Virtual address space for Linux EECS 213 Introduction to Computer SystemsNorthwestern University

25. Expansion slots I/O bus USB controller Graphics adapter Disk controller Network adapter Mouse Keyboard Display Disk Network 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 EECS 213 Introduction to Computer SystemsNorthwestern University

26. 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 SystemsNorthwestern University