Computer Systems Organization

Start Lecture #1

Chapter 0: Administrivia

I start at 0 so that when we get to chapter 1, the numbering will agree with the text.

0.1: Contact Information

• my-last-name AT nyu DOT edu (best method)
• http://cs.nyu.edu/~gottlieb
• 715 Broadway, Room 712
• 212 998 3344

0.2: Course Web Page

There is a web site for the course. You can find it from my home page, which is http://cs.nyu.edu/~gottlieb

• You can also find these lecture notes on the course home page. Please let me know if you can't find it.
• The notes are updated as bugs are found or improvements made.
• I will also produce a separate page for each lecture after the lecture is given. These individual pages might not get updated as quickly as the large page.

0.3: Textbook

The course has two texts

• Tanenbaum, "Structured Computer Organization" is the text for computer organization.
• We will also study the C programming language. You will need a book on C. I own, like, and will use Kernighan and Richie (the second is the creator of C). However, if you already own another C book, that is probably good enough.

0.4: Computer Accounts and Mailman Mailing List

• You are entitled to a computer account on one of the NYU sun machines. If you do not have one already, please get it asap.
• Sign up for the Mailman mailing list for the course. You can do so by clicking here.
• If you want to send mail just to me, use my-last-name AT nyu DOT edu not the mailing list.
• Questions on the labs should go to the mailing list. You may answer questions posed on the list as well. Note that replies are sent to the list.
• I will respond to all questions; if another student has answered the question before I get to it, I will confirm if the answer given is correct.
• Please use proper mailing list etiquette.
  • Send plain text messages rather than (or at least in addition to) html.
  • Use Reply to contribute to the current thread, but NOT to start another topic.
  • If quoting a previous message, trim off irrelevant parts.
  • Use a descriptive Subject: field when starting a new topic.
  • Do not use one message to ask two unrelated questions.
  • Do NOT make the mistake of sending your completed lab assignment to the mailing list. This is not a joke; several students have made this mistake in past semesters.
• As a favor to me, please do NOT top post, that is, when replying, I ask that you either place your reply after the original text or interspersed with it.
  • I know that there are differing opinions on top posting, but I find it very hard to follow conversations that way.
  • Exception: I realize Blackberry users must top post.

0.5: Grades

Grades are based on the labs, midterm, and the final exam, with each very important. The weighting will be approximately
30%*LabAverage + 30%*MidtermExam + 40%*FinalExam> (but see homeworks below).

0.6: The Upper Left Board

I use the upper left board for lab/homework assignments and announcements. I should never erase that board. Viewed as a file it is group readable (the group is those in the room), appendable by just me, and (re-)writable by no one. If you see me start to erase an announcement, let me know.

I try very hard to remember to write all announcements on the upper left board and I am normally successful. If, during class, you see that I have forgotten to record something, please let me know. HOWEVER, if I forgot and no one reminds me, the assignment has still been given.

0.7: Homeworks and Labs

I make a distinction between homeworks and labs.

Labs are

• Required.
• Due several lectures later (date given on assignment).
• Graded and form part of your final grade.
• Penalized for lateness. The penalty is 1 point per day up to 30 days; then 2 points per day.
• Normally computer programs you must write.

Homeworks are

• Optional.
• Due the beginning of Next lecture.
• Not accepted late.
• Mostly from the book(s).
• Collected and returned.
• Able to help, but not hurt, your grade.

0.7.1: Homework Numbering

Homeworks are numbered by the class in which they are assigned. So any homework given today is homework #1. Even if I do not give homework today, the homework assigned next class will be homework #2. Unless I explicitly state otherwise, all homeworks assignments can be found in the class notes. So the homework present in the notes for lecture #n is homework #n (even if I inadvertently forgot to write it to the upper left board).

0.7.2: Doing Labs on non-NYU Systems

You may solve lab assignments on any system you wish, but ...

• You are responsible for any non-nyu machine. I extend deadlines if the nyu machines are down, not if yours are.
• Be sure to test your assignments on the nyu systems. In an ideal world, a program written in a high level language like Java, C, or C++ that works on your system would also work on the NYU system used by the grader. Sadly, this ideal is not always achieved despite marketing claims that it is achieved. So, although you may develop your lab on any system, you must ensure that it compiles and runs on the nyu system assigned to the course.
• If somehow your assignment is misplaced by me and/or a grader, we need a to have some timestamp ON AN NYU SYSTEM that can be used to verify the date the lab was completed.
• When you complete a lab and have it on an nyu system, email the lab to the grader and copy yourself on that message. Please use one of the following two methods of mailing the lab.
  1. Send the mail from your CIMS account. (Not all students have a CIMS account.)
  2. Use the request receipt feature from home.nyu.edu or mail.nyu.edu and select the when delivered option.
  Keep the copy until you have received your grade on the assignment. I realize that I am being paranoid about this. It is rare for labs to get misplaced, but they sometimes do and I really don't want to be in the middle of an I sent it ... I never received it debate. Thank you.

0.7.3: Obtaining Help with the Labs

Good methods for obtaining help include

1. Asking me during office hours (see web page for my hours).
2. Asking the mailing list.
3. Asking another student, but ...
   Your lab must be your own.
   That is, each student must submit a unique lab. Naturally, simply changing comments, variable names, etc. does not produce a unique lab.

0.7.4: Computer Language Used for Labs

Each lab will indicate the language that must be used.

0.8: A Grade of Incomplete

The rules for incompletes and grade changes are set by the school> and not the department or individual faculty member.> The rules set by CAS can be found in , which states:

The grade of I (Incomplete) is a temporary grade that indicates that the student has, for good reason, not completed all of the course work but that there is the possibility that the student will eventually pass the course when all of the requirements have been completed. A student must ask the instructor for a grade of I, present documented evidence of illness or the equivalent, and clarify the remaining course requirements with the instructor.

The incomplete grade is not awarded automatically. It is not used when there is no possibility that the student will eventually pass the course. If the course work is not completed after the statutory time for making up incompletes has elapsed, the temporary grade of I shall become an F and will be computed in the student's grade point average.

All work missed in the fall term must be made up by the end of the following spring term. All work missed in the spring term or in a summer session must be made up by the end of the following fall term. Students who are out of attendance in the semester following the one in which the course was taken have one year to complete the work. Students should contact the College Advising Center for an Extension of Incomplete Form, which must be approved by the instructor. Extensions of these time limits are rarely granted.

Once a final (i.e., non-incomplete) grade has been submitted by the instructor and recorded on the transcript, the final grade cannot be changed by turning in additional course work.

0.9 Academic Integrity Policy

This email from the assistant director, describes the policy.

    Dear faculty,

    The vast majority of our students comply with the
    department's academic integrity policies; see

      www.cs.nyu.edu/web/Academic/Undergrad/academic_integrity.html
      www.cs.nyu.edu/web/Academic/Graduate/academic_integrity.html

    Unfortunately, every semester we discover incidents in
    which students copy programming assignments from those of
    other students, making minor modifications so that the
    submitted programs are extremely similar but not identical.

    To help in identifying inappropriate similarities, we
    suggest that you and your TAs consider using Moss, a
    system that automatically determines similarities between
    programs in several languages, including C, C++, and Java.
    For more information about Moss, see:

      http://theory.stanford.edu/~aiken/moss/

    Feel free to tell your students in advance that you will be
    using this software or any other system.  And please emphasize,
    preferably in class, the importance of academic integrity.

    Rosemary Amico
    Assistant Director, Computer Science
    Courant Institute of Mathematical Sciences
  

Remark: The chapter/section numbers for the material on C, agree with Kernighan and Plauger. However, the material is quite standard so, as mentioned before, if you already own a C book that you like, it should be fine.

Chapter 1: A Tutorial Introduction

Since Java includes much of C, my treatment can be very brief for the parts in common (e.g., control structures).

1.1: Getting Started

Hello World

  #include <stdio.h>
  main() {
    printf("Hello, world\n");
  }

• C programs consist of functions, which contain statements, and variables, which stores values.
• All complete programs must have a main function; your program begins execution there.
• # introduces preprocessor directives, #include is most common.
  #include <stdio.h> tells the preprocessor to look in the standard place (due to the <>) for a file named stdio.h and include it right here. That file contains the declaration of printf().
• printf() produces formatted output. The easiest case is simply a character string as shown here (\n causes a newline to be printed).

1.2: Variables and Arithmetic Expressions

1.3: The For Statement

1.4 Symbolic Constants

Fahrenheight-Celsius

  #include <stdio.h>
  main() {
    int F, C;
    int lo=0, hi=300, incr=20;
  
    for (F=lo; F<=hi; F+=incr) {
      C = 5 * (F-32) / 9;
      printf("%d\t%d\n", F, C);
    }
  }

• C has int, char, short, long, double, float
• %d means the next argument is (treated as) an int; convert it from the internal form (two's complement binary) to printable form (ascii, unicode, ...).
• %d uses the right amount of space (i.e., leaves one blank.
• \t is a tab.
• printf() uses varargs, variable number of arguments. Note that the value of the first argument determines the number of additional arguments.
• Would be better if numbers were right justified. We must know how much space to use; in this case I know 3 digits are enough.
• Should use floating point.

Floating Point Fahrenheight-Celcius

#include <stdio.h>
#define LO 0
#define HI 300
#define INCR 20
main() {
      int F;
      for (F=LO; F<=HI; F+=INCR) {
          printf("%3d\t%5.1f\n", F, (F-32)*(5.0/9.0));
      }
  }

• Note (5.0)/(9.0) to get floating point divide
• Note %5.1f. 1 digit after the decimal point 5=3+1+1 total.
• Call to printf() now contains an expression instead of a simple variable.
• #define to introduce symbolic constants. By convention these are all caps.

1.5: Character Input and Output

getchar() / putchar()

The simplest (i.e., most primitive form of character I/O is getchar() and putchar(), which read and print a single character.

1.5.1: File Copying

File copy is conceptually trivial: getchar() a char and then putchar() the char until eof. The code is on the right and does require some comment despite is brevity.

#include <stdio.h>
main() {
    int c;
    while ((c = getchar()) != EOF)
	putchar(c);
}
  

• getchar() returns an int not a char! That is done so that we can return EOF, which is not a char (and cannot by a char, why?); it is an int (in fact it is -1).
• C is an expression language, statements return values. In particular, an assignment statement returns the value of its RHS. This explains the condition part of the while statement, once you notice the extra parens, which are definitely not extra.
• getchar() reads from stdin and putchar() writes to stdout.
• Illustrate in class how to use stdin/stdout and redirection.

Homework: Write a (C-language) program to print the value of EOF. (This is 1-7 in the book but I realize not everyone will have the book so I will type them in.)

Homework: (1-9) Write a program to copy its input to its output, replacing each string of one or more blanks by a single blank.

1.5.2: Character Counting

1.5.3: Line Counting

1.5.4: Word Counting

The Unix wc Program

The Unix wc program prints the number of characters, words, and lines in the input. It is clear what the number of characters means. The number of lines is the number of newlines (so if the last line doesn't end in a newline, it doesn't count). The number of words is less clear. In particular, what should be the word separators?

#include <stdio.h>
#define WITHIN   1
#define OUTSIDE  0
main() {
  int c, num_lines, num_words, num_chars, within_or_outside;
  within_or_outside = OUTSIDE; /* C doesn't have Boolean type */
  num_lines = num_words = num_chars = 0;
  while ((c = getchar()) != EOF) {
    ++num_chars;
    if (c == '\n')
      ++num_lines;
    if (c == ' ' || c == '\n' || c == '\t')
      within_or_outside = OUTSIDE;
    else if (within_or_outside == OUTSIDE) { /* at beginning word */
      ++num_words;
      within_or_outside = WITHIN;
    }
  }
  printf("%d %d %d\n", num_lines, num_words, num_chars);
}

• In this program we say blank, newline, and tab are the only word separators.
• C doesn't have a real Boolean type. Instead int is used; 0 is false; everything else is true.
• The key idea in the program, which is independent of the language used, is to keep track of when we are within a word and to bump the word counter at the the start of a new word.
  • The program begins outside a word.
  • Whenever it encounters a separator, it becomes outside.
  • Whenever it encounters a non-separator (i.e., a word constituent) and was outside, then it has found the start of a new word. This puts the program within a word and is when it bumps the word counter.
• Java if-then-else same as C.
  Same for while and do / while.
  Same for switch / case.
  Same for continue, break, and return.

Homework: (1-12) Write a program that prints its input one word per line.