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Computer Organization CENG331 Section 3, Fall 2012-2013 1 st Lecture

Computer Organization CENG331 Section 3, Fall 2012-2013 1 st Lecture. Instructor: Erol Şahin. Acknowledgement: Most of the slides are adapted from the ones prepared by R.E. Bryant, D.R. O’Hallaron , G. Kesden and Markus Püschel of Carnegie-Mellon Univ. Overview. Course theme

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Computer Organization CENG331 Section 3, Fall 2012-2013 1 st Lecture

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  1. Computer OrganizationCENG331 Section 3, Fall 2012-20131st Lecture Instructor: ErolŞahin • Acknowledgement: Most of the slides are adapted from the ones prepared • by R.E. Bryant, D.R. O’Hallaron, G. Kesden and Markus Püschel of • Carnegie-Mellon Univ.

  2. Overview • Course theme • Five realities • How the course fits into the CENG curriculum • Logistics

  3. Course Theme:Abstraction Is Good But Don’t Forget Reality • Most CENG courses emphasize abstraction • Abstract data types • Asymptotic analysis • These abstractions have limits • Especially in the presence of bugs • Need to understand details of underlying implementations • Useful outcomes • Become more effective programmers • Able to find and eliminate bugs efficiently • Able to understand and tune for program performance • Prepare for later “systems” classes in CENG • Compilers, Operating Systems, Networks, Embedded Systems

  4. Great Reality #1: Int’s are not Integers, Float’s are not Reals • Example 1: Is x2 ≥ 0? • Float’s: Yes! • Int’s: • 40000 * 40000 --> 1600000000 • 50000 * 50000 --> ?? • Example 2: Is (x + y) + z = x + (y + z)? • Unsigned & Signed Int’s: Yes! • Float’s: • (1e20 + -1e20) + 3.14 --> 3.14 • 1e20 + (-1e20 + 3.14) --> ??

  5. Code Security Example • Similar to code found in FreeBSD’s implementation of getpeername • There are legions of smart people trying to find vulnerabilities in programs /* Kernel memory region holding user-accessible data */ #define KSIZE 1024 char kbuf[KSIZE]; /* Copy at most maxlen bytes from kernel region to user buffer */ intcopy_from_kernel(void *user_dest, intmaxlen) { /* Byte count len is minimum of buffer size and maxlen */ intlen = KSIZE < maxlen ? KSIZE : maxlen; memcpy(user_dest, kbuf, len); return len; }

  6. Typical Usage /* Kernel memory region holding user-accessible data */ #define KSIZE 1024 char kbuf[KSIZE]; /* Copy at most maxlen bytes from kernel region to user buffer */ int copy_from_kernel(void *user_dest, int maxlen) { /* Byte count len is minimum of buffer size and maxlen */ int len = KSIZE < maxlen ? KSIZE : maxlen; memcpy(user_dest, kbuf, len); return len; } #define MSIZE 528 void getstuff() { char mybuf[MSIZE]; copy_from_kernel(mybuf, MSIZE); printf(“%s\n”, mybuf); }

  7. Malicious Usage /* Kernel memory region holding user-accessible data */ #define KSIZE 1024 char kbuf[KSIZE]; /* Copy at most maxlen bytes from kernel region to user buffer */ int copy_from_kernel(void *user_dest, int maxlen) { /* Byte count len is minimum of buffer size and maxlen */ int len = KSIZE < maxlen ? KSIZE : maxlen; memcpy(user_dest, kbuf, len); return len; } #define MSIZE 528 void getstuff() { char mybuf[MSIZE]; copy_from_kernel(mybuf, -MSIZE); . . . }

  8. Computer Arithmetic • Does not generate random values • Arithmetic operations have important mathematical properties • Cannot assume all “usual” mathematical properties • Due to finiteness of representations • Integer operations satisfy “ring” properties • Commutativity, associativity, distributivity • Floating point operations satisfy “ordering” properties • Monotonicity, values of signs • Observation • Need to understand which abstractions apply in which contexts • Important issues for compiler writers and serious application programmers

  9. Great Reality #2: You’ve Got to Know Assembly • Chances are, you’ll never write program in assembly • Compilers are much better & more patient than you are • But: Understanding assembly key to machine-level execution model • Behavior of programs in presence of bugs • High-level language model breaks down • Tuning program performance • Understand optimizations done/not done by the compiler • Understanding sources of program inefficiency • Implementing system software • Compiler has machine code as target • Operating systems must manage process state • Creating / fighting malware • x86 assembly is the language of choice!

  10. Assembly Code Example • Time Stamp Counter • Special 64-bit register in Intel-compatible machines • Incremented every clock cycle • Read with rdtsc instruction • Application • Measure time (in clock cycles) required by procedure • double t; • start_counter(); • P(); • t = get_counter(); • printf("P required %f clock cycles\n", t);

  11. asm ( “assembly instructions” : output operands //optional : input operands //optional : list of clobbered regs //opt.. ); Code to Read Counter • Write small amount of assembly code using GCC’s asm facility • Inserts assembly code into machine code generated by compiler static unsigned cyc_hi = 0; static unsigned cyc_lo = 0; /* Set *hi and *lo to the high and low order bits of the cycle counter. */ void access_counter(unsigned *hi, unsigned *lo) { asm("rdtsc; movl %%edx,%0; movl %%eax,%1" : "=r" (*hi), "=r" (*lo) : : "%edx", "%eax"); }

  12. Great Reality #3: Memory MattersRandom Access Memory Is an Unphysical Abstraction • Memory is not unbounded • It must be allocated and managed • Many applications are memory dominated • Memory referencing bugs especially pernicious • Effects are distant in both time and space • Memory performance is not uniform • Cache and virtual memory effects can greatly affect program performance • Adapting program to characteristics of memory system can lead to major speed improvements

  13. volatile keyword is intended to prevent the compiler from applying any optimizations on the code that assume values of variables cannot change "on their own." Memory Referencing Bug Example double fun(int i) { volatile double d[1] = {3.14}; volatile long int a[2]; a[i] = 1073741824; /* Possibly out of bounds */ return d[0]; } fun(0) –> 3.14 fun(1) –> 3.14 fun(2) –> 3.1399998664856 fun(3) –> 2.00000061035156 fun(4) –> 3.14, then segmentation fault

  14. Saved State d7 … d4 d3 … d0 a[1] a[0] Memory Referencing Bug Example double fun(inti) { volatile double d[1] = {3.14}; volatile long int a[2]; a[i] = 1073741824; /* Possibly out of bounds */ return d[0]; } fun(0) –> 3.14 fun(1) –> 3.14 fun(2) –> 3.1399998664856 fun(3) –> 2.00000061035156 fun(4) –> 3.14, then segmentation fault Explanation: 4 3 Location accessed by fun(i) 2 1 0

  15. Memory Referencing Errors • C and C++ do not provide any memory protection • Out of bounds array references • Invalid pointer values • Abuses of malloc/free • Can lead to nasty bugs • Whether or not bug has any effect depends on system and compiler • Action at a distance • Corrupted object logically unrelated to one being accessed • Effect of bug may be first observed long after it is generated • How can I deal with this? • Program in Java or ML • Understand what possible interactions may occur • Use or develop tools to detect referencing errors

  16. Memory System Performance Example • Hierarchical memory organization • Performance depends on access patterns • Including how step through multi-dimensional array void copyij(intsrc[2048][2048], intdst[2048][2048]) { inti,j; for (i = 0; i < 2048; i++) for (j = 0; j < 2048; j++) dst[i][j] = src[i][j]; } void copyji(intsrc[2048][2048], intdst[2048][2048]) { inti,j; for (j = 0; j < 2048; j++) for (i = 0; i < 2048; i++) dst[i][j] = src[i][j]; } 21 times slower(Pentium 4)

  17. The Memory Mountain Intel Core i7 2.67 GHz 32 KB L1 d-cache 256 KB L2 cache 8 MB L3 cache

  18. Great Reality #4: There’s more to performance than asymptotic complexity • Constant factors matter too! • And even exact op count does not predict performance • Easily see 10:1 performance range depending on how code written • Must optimize at multiple levels: algorithm, data representations, procedures, and loops • 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

  19. Example Matrix Multiplication • Standard desktop computer, vendor compiler, using optimization flags • Both implementations have exactly the same operations count (2n3) • What is going on? 160x Best code (K. Goto) Triple loop

  20. MMM Plot: Analysis Multiple threads: 4x Vector instructions: 4x Memory hierarchy and other optimizations: 20x • Reason for 20x: Blocking or tiling, loop unrolling, array scalarization, instruction scheduling, search to find best choice • Effect: less register spills, less L1/L2 cache misses, less TLB misses

  21. Great Reality #5: 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 • Many system-level issues arise in presence of network • Concurrent operations by autonomous processes • Coping with unreliable media • Cross platform compatibility • Complex performance issues

  22. Role within CENG Curriculum CENG334 Operating Systems CS 352 Databases CS 444 Compilers CS 477 Computer Graphics CENG336 Embedded Systems Processes Mem. Mgmt Machine Code Execution Model Memory System Data Reps. Memory Model Arithmetic CENG331 • Computer Organization CENG140 C(++) Programming

  23. Course Perspective • Most Systems Courses are Builder-Centric • Computer Architecture • Design pipelined processor in Verilog • Operating Systems • Implement large portions of operating system • Compilers • Write compiler for simple language • Networking • Implement and simulate network protocols

  24. Course Perspective (Cont.) • Our 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 • 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

  25. Teaching staff • Instructor • Dr. ErolSahin • Location: B-111, Tel: 210 5539, • E-mail: erol@ceng.metu.edu.tr • Office hours: By appointment. • TA’s • FatihGokce (E-mail: fgokce@ceng.metu.edu.tr) • AsliGenctav (E-mail: asli@ceng.metu.edu.tr)

  26. Textbooks • Randal E. Bryant and David R. O’Hallaron, • “Computer Systems: A Programmer’s Perspective, Second Edition”, Prentice Hall 2011. • http://csapp.cs.cmu.edu • This book really matters for the course! • How to solve labs • Practice problems typical of exam problems

  27. Course Components • Lectures • Higher level concepts • Assignments (3) • The heart of the course • Provide in-depth understanding of an aspect of systems • Programming and measurement • Exams (midterm + final) • Test your understanding of concepts & mathematical principles

  28. Policies: Grading • Midterm 1: 25%. • Midterm 2: 25% • Assignments: 20%. • 4 homeworks • Precondition for entering final exam: • Accumulate 25/100 overall from midterms and homeworks • Final: 30%.

  29. Assignments • Binary bomb: • Defuse a binary bomb by disassembling and reverse engineering the program. • Buffer overflow: • Modify the run-time behaviour of a binary executable by using the buffer overflow bug. • Architecture: • Modify the HCL description of a processor to add new instructions. • Performance: • Optimize the performance of a function. Details regarding the scheduling and grading of these assignments will be announced later.

  30. Assignment Rationale • Each assignment should have a well-defined goal such as solving a puzzle or winning a contest. • Doing an assignment should result in new skills and concepts • We try to use competition in a fun and healthy way. • Set a reasonable threshold for full credit. • Post intermediate results (anonymized) on Web page for glory!

  31. Communication • Class Web Pages • Web: http://kovan.ceng.metu.edu.tr/~erol/Courses/CENG331 • Copies of lectures, exams, solutions • http://cow.ceng.metu.edu.tr/ • Assignments, grades etc. • Newsgroup • news://metu.ceng.course.331 • Announcements about the course, clarifications to assignments, general discussion • Communication • Questions that are general should be posted to the newsgroup. Please put [Section 3 ] on the subject line of your posting. • If you have a specific question you can send an e-mail to the instructors or to your teaching assistants. However make sure that the subject line starts with CENG331 [capital letters, and no spaces] to get faster reply.

  32. Policies • Late assignments: • Late submission policy will be announced for each assignment. • Academic dishonesty: • All assignments submitted should be fully your own. We have a zero tolerance policy on cheating and plagiarism. Your work will be regularly checked for such misconduct and persecuted. • We would like to remind you that, if found guilty, the legal code of the university proposes a minimum of six month expulsion from the university.

  33. Cheating • What is cheating? • Sharing code: either by copying, retyping, looking at, or supplying a copy of a file. • Coaching: helping your friend to write a lab, line by line. • Copying code from previous course or from elsewhere on WWW • Only allowed to use code we supply, or from CS:APP website • What is NOT cheating? • Explaining how to use systems or tools. • Helping others with high-level design issues. • Penalty for cheating: • Removal from course with failing grade. • Detection of cheating: • We do check and our tools for doing this are much better than you think!

  34. If you don’t want to cry at the end of the semester.. • Keep in mind that this is a MUST course! • If you fail to get passing grades you may lose a year! • No extra exams, or extra time to submit assignments after grading.

  35. We’ll have fun!

  36. Conclusion • 5 Great Realities • Ints are not Integers, Floats are not Reals • You’ve Got to Know Assembly • Memory Matters • There’s more to performance than asymptotic complexity • Computers do more than execute programs Abstraction Is Good But Don’t Forget Reality

  37. A Tour of Computer SystemsCENG331 Section 1 & 2, Fall 2011-2012 Instructor: ErolŞahin • Acknowledgement: Most of the slides are adapted from the ones prepared • by R.E. Bryant, D.R. O’Hallaron of Carnegie-Mellon Univ.

  38. hello.c #include <stdio.h> int main() { printf(“Hello World”); }

  39. Compilation of hello.c 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)‏

  40. Preprocessing # 1 "hello.c" # 1 "<built-in>" # 1 "<command line>" # 1 "hello.c" # 1 "/usr/include/stdio.h" 1 3 4 …………………………………….. typedef unsigned char __u_char; typedef unsigned short int __u_short; typedef unsigned int __u_int; typedef unsigned long int __u_long; ……………………………………….. int main() { printf(“Hello World”); } Pre- processor (cpp)‏ hello.c hello.i Source program (text)‏ Modified source program (text)‏ #include <stdio.h> int main() { printf(“Hello World”); } cpp hello.c > hello.i

  41. Compiler .file "hello.c" .section .rodata .LC0: .string "Hello World" .text .globl main .type main, @function main: pushl %ebp movl %esp, %ebp subl $8, %esp andl $-16, %esp movl $0, %eax addl $15, %eax addl $15, %eax shrl $4, %eax sall $4, %eax subl %eax, %esp subl $12, %esp pushl $.LC0 call printf addl $16, %esp leave ret .size main, .-main .section .note.GNU-stack,"",@progbits .ident "GCC: (GNU) 3.4.1" # 1 "hello.c" # 1 "<built-in>" # 1 "<command line>" # 1 "hello.c" # 1 "/usr/include/stdio.h" 1 3 4 …………………………………….. typedef unsigned char __u_char; typedef unsigned short int __u_short; typedef unsigned int __u_int; typedef unsigned long int __u_long; ……………………………………….. int main() { printf(“Hello World”); } Compiler (cc1)‏ hello.s hello.i gcc -Wall -S hello.i > hello.s

  42. Assembler Assembler (as)‏ hello.s hello.o .file "hello.c" .section .rodata .LC0: .string "Hello World" .text .globl main .type main, @function main: pushl %ebp movl %esp, %ebp subl $8, %esp andl $-16, %esp movl $0, %eax addl $15, %eax addl $15, %eax shrl $4, %eax sall $4, %eax subl %eax, %esp subl $12, %esp pushl $.LC0 call printf addl $16, %esp leave ret .size main, .-main .section .note.GNU-stack,"",@progbits .ident "GCC: (GNU) 3.4.1" 0000500 nulnulnulnul esc nulnulnul ht nulnulnulnulnulnulnul 0000520 nulnulnulnuldetxnulnuldlenulnulnul ht nulnulnul 0000540 sohnulnulnuleotnulnulnulbsnulnulnul % nulnulnul 0000560 sohnulnulnuletxnulnulnulnulnulnulnuldnulnulnul 0000600 nulnulnulnulnulnulnulnulnulnulnulnuleotnulnulnul 0000620 nulnulnulnul + nulnulnulbsnulnulnuletxnulnulnul 0000640 nulnulnulnuldnulnulnulnulnulnulnulnulnulnulnul 0000660 nulnulnulnuleotnulnulnulnulnulnulnul 0 nulnulnul 0000700 sohnulnulnulstxnulnulnulnulnulnulnuldnulnulnul 0000720 ff nulnulnulnulnulnulnulnulnulnulnulsohnulnulnul 0000740 nulnulnulnul 8 nulnulnulsohnulnulnulnulnulnulnul 0000760 nulnulnulnulpnulnulnulnulnulnulnulnulnulnulnul 0001000 nulnulnulnulsohnulnulnulnulnulnulnul H nulnulnul 0001020 sohnulnulnulnulnulnulnulnulnulnulnulpnulnulnul 0001040 2 nulnulnulnulnulnulnulnulnulnulnulsohnulnulnul 0001060 nulnulnulnul dc1 nulnulnuletxnulnulnulnulnulnulnul 0001100 nulnulnulnul " nulnulnul Q nulnulnulnulnulnulnul 0001120 nulnulnulnulsohnulnulnulnulnulnulnulsohnulnulnul 0001140 stxnulnulnulnulnulnulnulnulnulnulnul , stxnulnul 0001160 sp nulnulnulnlnulnulnulbsnulnulnuleotnulnulnul 0001200 dlenulnulnul ht nulnulnuletxnulnulnulnulnulnulnul 0001220 nulnulnulnul L etxnulnulnaknulnulnulnulnulnulnul 0001240 nulnulnulnulsohnulnulnulnulnulnulnulnulnulnulnul 0001260 nulnulnulnulnulnulnulnulnulnulnulnulsohnulnulnul 0001300 nulnulnulnulnulnulnulnuleotnulq del nulnulnulnul 0001320 nulnulnulnulnulnulnulnuletxnulsohnulnulnulnulnul 0001340 nulnulnulnulnulnulnulnuletxnuletxnulnulnulnulnul 0001360 nulnulnulnulnulnulnulnuletxnuleotnulnulnulnulnul 0001400 nulnulnulnulnulnulnulnuletxnulenqnulnulnulnulnul 0001420 nulnulnulnulnulnulnulnuletxnulacknulnulnulnulnul 0001440 nulnulnulnulnulnulnulnuletxnulbelnul ht nulnulnul 0001460 nulnulnulnul . nulnulnul dc2 nulsohnul so nulnulnul 0001500 nulnulnulnulnulnulnulnuldlenulnulnulnulhel 0001520 lo . cnulm a innulprintf 0001540 nulnulnulnul sp nulnulnulsohenqnulnul % nulnulnul 0001560 stx ht nulnul 0001564 as hello.s -o hello.o od –a hello.o

  43. Linker printf.o Linker (ld)‏ hello.o hello Relocatable object programs (binary)‏ Executable object program (binary)‏ 0000500 nulnulnulnul esc nulnulnul ht nulnulnulnulnulnulnul 0000520 nulnulnulnuldetxnulnuldlenulnulnul ht nulnulnul 0000540 sohnulnulnuleotnulnulnulbsnulnulnul % nulnulnul 0000560 sohnulnulnuletxnulnulnulnulnulnulnuldnulnulnul 0000600 nulnulnulnulnulnulnulnulnulnulnulnuleotnulnulnul 0000620 nulnulnulnul + nulnulnulbsnulnulnuletxnulnulnul 0000640 nulnulnulnuldnulnulnulnulnulnulnulnulnulnulnul 0000660 nulnulnulnuleotnulnulnulnulnulnulnul 0 nulnulnul 0000700 sohnulnulnulstxnulnulnulnulnulnulnuldnulnulnul 0000720 ff nulnulnulnulnulnulnulnulnulnulnulsohnulnulnul 0000740 nulnulnulnul 8 nulnulnulsohnulnulnulnulnulnulnul 0000760 nulnulnulnulpnulnulnulnulnulnulnulnulnulnulnul 0001000 nulnulnulnulsohnulnulnulnulnulnulnul H nulnulnul 0001020 sohnulnulnulnulnulnulnulnulnulnulnulpnulnulnul 0001040 2 nulnulnulnulnulnulnulnulnulnulnulsohnulnulnul 0001060 nulnulnulnul dc1 nulnulnuletxnulnulnulnulnulnulnul 0001100 nulnulnulnul " nulnulnul Q nulnulnulnulnulnulnul 0001120 nulnulnulnulsohnulnulnulnulnulnulnulsohnulnulnul 0001140 stxnulnulnulnulnulnulnulnulnulnulnul , stxnulnul 0001160 sp nulnulnulnlnulnulnulbsnulnulnuleotnulnulnul 0001200 dlenulnulnul ht nulnulnuletxnulnulnulnulnulnulnul 0001220 nulnulnulnul L etxnulnulnaknulnulnulnulnulnulnul 0001240 nulnulnulnulsohnulnulnulnulnulnulnulnulnulnulnul 0001260 nulnulnulnulnulnulnulnulnulnulnulnulsohnulnulnul 0001300 nulnulnulnulnulnulnulnuleotnulq del nulnulnulnul 0001320 nulnulnulnulnulnulnulnuletxnulsohnulnulnulnulnul 0001340 nulnulnulnulnulnulnulnuletxnuletxnulnulnulnulnul 0001360 nulnulnulnulnulnulnulnuletxnuleotnulnulnulnulnul 0001400 nulnulnulnulnulnulnulnuletxnulenqnulnulnulnulnul 0001420 nulnulnulnulnulnulnulnuletxnulacknulnulnulnulnul 0001440 nulnulnulnulnulnulnulnuletxnulbelnul ht nulnulnul 0001460 nulnulnulnul . nulnulnul dc2 nulsohnul so nulnulnul 0001500 nulnulnulnulnulnulnulnuldlenulnulnulnulhel 0001520 lo . cnulm a innulprintf 0001540 nulnulnulnul sp nulnulnulsohenqnulnul % nulnulnul 0001560 stx ht nulnul 0001564 gcc hello.o –o hello 0000000 del E L F sohsohsohnulnulnulnulnulnulnulnulnul 0000020 stxnuletxnulsohnulnulnul @ stxeotbs 4 nulnulnul 0000040 X crnulnulnulnulnulnul 4 nul sp nulbelnul ( nul 0000060 ! nulrsnulacknulnulnul 4 nulnulnul 4 nuleotbs 0000100 4 nuleotbs ` nulnulnul ` nulnulnulenqnulnulnul 0000120 eotnulnulnuletxnulnulnul dc4 sohnulnul dc4 soheotbs 0000140 dc4 soheotbs dc3 nulnulnul dc3 nulnulnuleotnulnulnul 0000160 sohnulnulnulsohnulnulnulnulnulnulnulnulnuleotbs 0000200 nulnuleotbsbseotnulnulbseotnulnulenqnulnulnul 0000220 nuldlenulnulsohnulnulnulbseotnulnulbs dc4 eotbs 0000240 bs dc4 eotbsnulsohnulnuleotsohnulnulacknulnulnul 0000260 nuldlenulnulstxnulnulnul dc4 eotnulnul dc4 dc4 eotbs 0000300 dc4 dc4 eotbs H nulnulnul H nulnulnulacknulnulnul 0000320 eotnulnulnuleotnulnulnul ( sohnulnul ( soheotbs 0000340 ( soheotbs sp nulnulnul sp nulnulnuleotnulnulnul 0000360 eotnulnulnul Q etdnulnulnulnulnulnulnulnul 0000400 nulnulnulnulnulnulnulnulnulnulnulnulacknulnulnul 0000420 eotnulnulnul / lib / ld - linu 0000440 x . so . 2 nulnuleotnulnulnuldlenulnulnul 0000460 sohnulnulnul G N U nulnulnulnulnulstxnulnulnul 0000500 stxnulnulnulenqnulnulnuletxnulnulnulacknulnulnul 0000520 enqnulnulnulsohnulnulnuletxnulnulnulnulnulnulnul 0000540 nulnulnulnulnulnulnulnulstxnulnulnulnulnulnulnul …………………………………………………………………………….. od –a hello

  44. Finally… • $ gcchello.o -o hello • $ ./hello • Hello World$

  45. How do you say “Hello World”?

  46. Typical Organization of System 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

  47. CPU 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" Reading hello command from keyboard

  48. 00•••0 FF•••F • • • Byte-Oriented Memory Organization • Programs Refer to Virtual Addresses • Conceptually very large array of bytes • Actually implemented with hierarchy of different memory types • System provides address space private to particular “process” • Program being executed • Program can clobber its own data, but not that of others • Compiler + Run-Time System Control Allocation • Where different program objects should be stored • All allocation within single virtual address space

  49. Machine Words • Machine Has “Word Size” • Nominal size of integer-valued data • Including addresses • Most current machines use 32 bits (4 bytes) words • Limits addresses to 4GB • Becoming too small for memory-intensive applications • High-end systems use 64 bits (8 bytes) words • Potential address space ≈ 1.8 X 1019 bytes • x86-64 machines support 48-bit addresses: 256 Terabytes • Machines support multiple data formats • Fractions or multiples of word size • Always integral number of bytes

  50. 0008 0012 0008 0004 0000 0000 32-bit Words 64-bit Words Bytes Addr. 0000 Addr = ?? 0001 0002 Addr = ?? 0003 0004 Addr = ?? 0005 0006 0007 0008 Addr = ?? 0009 0010 Addr = ?? 0011 0012 Addr = ?? 0013 0014 0015 Word-Oriented Memory Organization • Addresses Specify Byte Locations • Address of first byte in word • Addresses of successive words differ by 4 (32-bit) or 8 (64-bit)

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