File: Program

( 2014-11-09)


  1. “Greatest Common Divisor.” Rosetta Code Aug. 2014. Web. Link (remote) →
  2. “ENIAC’s Programmers.” 2011. Web. Link (remote) →
  3. Ceruzzi, Paul E. “The Stored Program Principle.” Computing: A Concise History. Cambridge, MA: MIT Press, 2012. 49–80. Print.
  4. ---. “The First Computers, 1935-1945.” Computing: A Concise History. Cambridge, MA: MIT Press, 2012. 23–48. Print.
  5. Colburn, Timothy R. “Software, Abstraction, And Ontology.” The Monist 82.1 (1999): 3–19. Web. Link (remote) →
  6. Da Cruz, Frank. “Programming The ENIAC.” Columbia University Computing History Nov. 2013. Web. Link (remote) →
  7. Downey, Allen. “Formal And Natural Languages.” Think Python: How to Think Like a Computer Scientist. Version 2.0.12. Needham, MA: Green Tea Press, 2013. 5–6. Web. Link (remote) →
  8. Erickson, LeeAnn, and Cynthia Baughman. “Top Secret Rosies: The Female Computers of World War II.” 2010. Web. Link (remote) →
  9. Knuth, Donald E. “Algorithm And Program; Information And Data.” Communications of the ACM 9.9 (1966): 654. Web. Link (remote) →
  10. Light, Jennifer S. “When Computers Were Women.” Technology and Culture 40.3 (1999): 455–483. Web. Link (remote) →
  11. Moye, William T. “ENIAC: The Army-Sponsored Revolution.” Jan. 1996. Web. Link (remote) →
  12. Rösler, Wolfram. “The Hello World Collection.” Sep. 2014. Web. Link (remote) →

What is a program?

Plain text that can be interpreted as instructions to perform a computational process

Hello world

The simplest program is a single instruction:

print "Hello world!"


def hello
    print 'Hello world!'
  • Here, a separate function
  • Like a dictionary definition

…and function calls

def hello
    print 'Hello world!'

  • Calling a function is like looking up and reading a dictionary definition
  • A programming language interpreter reads the definition and executes the instructions it contains

The double life of a program: three doubles

  • Ontological
    1. A static text artifact or product
    2. When executed, a dynamic computational process
  • Semantic
    1. As data
    2. As instructions
  • Legal
    1. Text, therefore protected by copyright
    2. Mechanism, therefore patentable

Layers of abstraction

“…the whole history of computer science has seen the careful construction of layer upon layer of distancing abstractions upon the basic foundation of zeros and ones. Each time a programmer writes and executes a high-level program, these layers are stripped away one by one in elaborate translations from talk of, say, chat rooms, to talk of windows, to talk of matrices, to talk of variables, registers, and memory addresses too, finally, zeros and ones. As an abstraction, this translation is complete and flawless. (Colburn 16)


Exercise: algorithm

  • Write an algorithm that will help someone find her or his way to our classroom
  • Write an algorithm for making the perfect sandwich (or the perfect lunch, if you don’t like sandwiches)

Algorithm as abstraction

  • An algorithm is an abstract computational method that exists “apart from any programming language.” (Knuth)

  • A program is a representation and a concrete “embodiment” of an algorithm in a particular language (Knuth)


Pseudocode example

If it is a weekday, then:
    If it is a weekday when this class meets, then:
        Get up
        For each cup in three cups of coffee:
            Drink cup
        Walk to campus
        Walk to the building where this class meets
        Walk to the classroom where this class meets
        Do something else
    Stay in bed

From “computer” to “programmer”

The word “computer” originally denoted a human occupation:

During the war, BRL [U.S. Army Ballistic Research Laboratory] recruited approximately two hundred women to work as computers, hand-calculating firing tables for rockets and artillery shells. (Light)

During and after WWII, the denotation of “computer” shifted to the electromechanical or electronic machine that automated and replaced that human occupation:

During World War II, a “computer” was a person who calculated artillery firing tables using a desk calculator. Six women “computers” were assigned to serve as ENIAC’s original programming group. Although most were college graduates, the “girls” were told that only “men” could get professional ratings. Finally, in November 1946, many of the women received professional ratings. (Moye)

ENIAC’s first application was to solve an important problem for the Manhatten [sic] Project. Involved were Nicholas Metropolis and Stanley Frankel from the Los Alamos National Laboratory, who worked with Eckert, Mauchly, and the women programmers. Captain (Dr.) Goldstine and his wife, Adele, taught Metropolis and Frankel how to program the machine, and the “girls” would come in and set the switches according to the prepared program. (Moye)

Stored program computing

  • Advantages of stored program computing architecture
    1. Preparing the program in advance and storing it as data enables faster execution
    2. Ability to treat program as data and modify it when you want to
      • Ability to operate on program data itself
      • Example: storing commonly used subroutines in advance and calling them from a program when they were needed
      • Such subroutines could be written in binary operation codes, then “called” by a program written in a higher-level code: for example, a code using words from the English language (“set,” “get,” “goto”, “print”), which are easier for humans to read and write

This is really the beginning of the history of what we now call “programming languages”:

By storing a program and data in a common high-speed memory, not only could programs be executed at electronic speeds; the programs could also be operated on as if they were data — the ancestor of today’s high-level languages compiled inside modern computers. (Ceruzzi)

Ceruzzi: the “stored program principle” was so influential that the referent of the word “computer” shifted once again. Now, it described electromechanical or electronic machines designed with a stored program architecture, rather than other designs:

The definition of computer thus changed, and to an extent it remains the one used today, with the criterion of programmability now extended to encompass the internal storage of that program in high-speed memory. (Ceruzzi)

Assemblers and alphanumeric assembly codes

EDSAC (University of Cambridge, 1949)

  • EDSAC provided a hard-wired assembler program stored in ROM, allowing the programmer to enter brief alphanumberic codes instead of coding in binary notation
  • The assembler performed the “translation” of those alphanumberic codes into binary code
  • This assembler program was called “initial orders” (it had two versions)
  • “Hello World” for EDSAC initial orders 1, from EDSAC Programming Tutorial:

      P1F O56F 
      *F HF EF LF LF OF 
      !F WF OF RF LF DF &F
  • These are the alphanumeric assembler codes for a “Hello world!” program written for EDSAC’s “initial orders” assembler 1
  • The first two lines are preparatory codes, stopping any prior process and clearing the memory
  • The remainder of the program directs the machine’s teleprinter to print a series of alphabetic charaters, the string “Hello world!”
  • They tell it to retrieve one character at a time from the character codes on the last two lines of the program, store them in memory, and then print them using the teleprinter


…a special kind of program, later called a compiler, would take as its input instructions written in a form that was familiar to human programmers and easy to grasp, and its output would be another program, this one written in the arcane codes that the hardware was able to decode. (Ceruzzi)

  • Terminology was in flux, and its took time for the meaning of the word “compiler” to stabilize
  • A compiler performed the same function as what was earlier sometimes called an “assembler”: translating higher-level codes that were easy for the programmer to write into lower-level machine codes
  • This amounts to writing in a “programming language,” instead of entering such operation codes

“Hello world!” written in the C programming language


    printf("Hello World");


Compiling the plain text file hello.c

$ gcc -v hello.c

Executing the object code produced by the compiler

$ ./a.out
Hello world!

From “compiler” to “programming language”

Eventually, the term “compiler” came to refer to a software program that performed that translation, while “programming language” came to refer to the particular code used by the programmer to write for the compiler

It was also around this time that these codes came to be called “languages,” because they shared many, though not all, characteristics with spoken languages. (Ceruzzi)

  • The analogy was based on the fact that natural languages and programming languages shared a few restricted attributes, such as syntactic rules
  • Programming languages have rules of syntax just as natural languages do, though in the case of programming languages the rules are deliberately designed, whereas in natural languages, we become aware of those rules only after learning to use them

FORTRAN (FORmula TRANslation), 1957

  • Compare the below with a more “direct” programming using EDSAC’s operation codes:

     PRINT *, "Hello World!"
  • This is a “Hello world!” program written in FORTRAN, the first higher-level programming language
  • Much more like English than the operation codes used to program EDSAC’s assembler

COBOL (COmmon Business-Oriented Language), 1958

  • Designed as a common business programming language
  • Used an even more extensively English-like syntax

FORTRAN and COBOL: algebraic notation vs. English-language prose


Conditional (if) statement that is true if value of a is larger than value of b:

IF A > B


  • In COBOL programming one might deliberately use use long value or variable names (EMPLOYEE-HOURS) instead of simple letter symbols (A, B)
  • One can use English prose expressions (GREATER THAN, MAXIMUM) rather than algebraic symbols

Clumsiness of the analogy between language and code

This is the beginning of a certain confusion caused by the analogy between code and human language

In the years that followed, researchers explored the relationship between machine and human language, and while COBOL was a significant milestone, it gave the illusion that it understood English better than it really did. (Paul Ceruzzi, A History of Modern Computing)

The word “language” turned out to be a dangerous term, implying much more than its initial users foresaw. The English word is derived from the French langue, meaning tongue, implying that it is spoken. Whatever other parallels there may be with natural language, computer languages are not spoken but written, according to a rigidly defined and precise syntax. (Paul Ceruzzi, A History of Modern Computing)

Natural languages

Downey, Elkner & Meyers, “Formal and Natural Languages” (Downey)

  1. Are spoken
  2. Were not designed
  3. Can be ambiguous and context-dependent in usage
  4. Are redundant and verbose or “noisy” as a result

Formal languages

Downey, Elkner & Meyers, “Formal and Natural Languages” (Downey)

  1. Are not spoken
  2. Were designed
  3. Were designed to be unambiguous in usage
  4. Are concise as a result

Programming languages

Downey, Elkner & Meyers, “Formal and Natural Languages” (Downey)

Programming languages are formal languages that were “designed to express computations”