Page 189 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes
Figure 9.2: Data and Instructions could be Stored on External Punched Cards, Which
were Kept in Order and Arranged in Program Decks

The invention of the von Neumann architecture allowed computer programs to be stored in
computer memory. Early programs had to be painstakingly crafted using the instructions
(elementary operations) of the particular machine, often in binary notation. Every model of
computer would likely use different instructions (machine language) to do the same task. Later,
assembly languages were developed that let the programmer specify each instruction in a text
format, entering abbreviations for each operation code instead of a number and specifying
addresses in symbolic form (e.g., ADD X, TOTAL). Entering a program in assembly language is
usually more convenient, faster, and less prone to human error than using machine language, but
because an assembly language is little more than a different notation for a machine language, any
two machines with different instruction sets also have different assembly languages.
In 1954, FORTRAN was invented; it was the first high level programming language to have a
functional implementation, as opposed to just a design on paper. (A high-level language is, in
very general terms, any programming language that allows the programmer to write programs
in terms that are more abstract than assembly language instructions, i.e. at a level of abstraction
“higher” than that of an assembly language.) It allowed programmers to specify calculations by
entering a formula directly (e.g. Y = X*2 + 5*X + 9). The program text, or source, is converted into
machine instructions using a special program called a compiler, which translates the FORTRAN
program into machine language. In fact, the name FORTRAN stands for “Formula Translation”.
Many other languages were developed, including some for commercial programming, such as
COBOL. Programs were mostly still entered using punched cards or paper tape. By the late 1960s,
data storage devices and computer terminals became inexpensive enough that programs could be
created by typing directly into the computers. Text editors were developed that allowed changes
and corrections to be made much more easily than with punched cards.

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