Page 208 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Unit 10: Programming Language

Today, assembly languages are considered very low level-that is, they are not as convenient for Notes
people to use as more recent languages. At the time they were developed, however, they were
considered a great leap forward. To replace the Is and Os used in machine language, assembly
languages use mnemonic codes, abbreviations that are easy to remember: A for Add, C for
Compare, MP for Multiply, STO for storing information in memory, and so on. Although these
codes are not English words, they are still- from the standpoint of human convenience-preferable
to numbers (Os and 1s) alone. Furthermore, assembly languages permit the use of names- perhaps
RATE or TOTAL-for memory locations instead of actual address numbers just like machine
language, each type of computer has its own assembly language.
The programmer who uses an assembly language requires a translator to convert the assembly
language program into machine language. The translator is an assembler program, also referred
to as an assembler. It takes the programs written in assembly language and turns them into
machine language. Programmers need not worry about the translating aspect; they need only
write programs in assembly language. The translation is taken care of by the assembler.
A translator is needed because machine language is the only language the
computer can actually execute.
Although assembly languages represent a step forward, they still have many
disadvantages. A key disadvantage is that assembly language is detailed in the
extreme, making assembly programming repetitive, tedious, and error prone.
This drawback is apparent in the program in Figure 7.7. Assembly language
may be easier to read than machine language, but it is still tedious.

10.2.3 High-Level Languages
The first widespread use of high-level languages in the early 1960s transformed programming
into something quite different from what it had been. Programs were written in an English-like
manner, thus making them more convenient to use. As a result, a programmer could accomplish
more with less effort, and programs could now direct much more complex tasks.

These so-called third-generation languages spurred the great increase in data processing that
characterized the 1960s and 1970s. During that time the number of mainframes in use increased
from hundreds to tens of thousands. The impact of third-generation languages on our society
has been enormous.
Of course, a translator is needed to translate the symbolic statements of a high-level language
into computer-executable machine language; this translator is usually a compiler. There are many
compilers for each language and one for each type of computer. Since the machine language
generated by one computer’s COBOL compiler, for instance, is not the machine language of some
other computer, it is necessary to have a COBOL compiler for each type of computer on which
COBOL programs are to be run. Keep in mind, however, that even though a given program would
be compiled to different machine language versions on different machines, the source program
itself-the COBOL version-can be essentially identical on each machine.

Some languages are created to serve a specific purpose, such as controlling industrial robots or
creating graphics. Many languages, however, are extraordinarily flexible and are considered to
be general-purpose. In the past the majority of programming applications were written in BASIC,
FORTRAN, or COBOL-all general-purpose languages. In addition to these three, another popular
high-level language is C, which we will discuss later.

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