High- and Low-Level Languages
Key definitions
Computer program
A list of instructions that enable a computer to perform a specific task.
Translator
Translators convert a program into binary instructions that computers
can understand.
Computer programs
A computer program is a list of instructions that enable a computer to perform a specific
task. Computer programs can be written in high-level languages and low-level languages
depending on the task to be performed and the computer to be used. Most
programmers write programs in high-level languages.
High-level languages
High-level languages enable a programmer to focus on the problem to be solved and
require no knowledge of the hardware and instruction set of the computer that will use
the program. High-level programming languages are portable and can be used on
different types of computer.
Low-level languages
Low-level languages relate to the specific architecture and hardware of a particular type
of computer. Low-level languages can refer to machine code, the binary instructions that
a computer understands, or assembly language that needs to be translated into machine
code.
Assembly languages
Assembly language is a low-level programming language that needs to be translated into
machine code by an assembler.
Machine code
Machine code is the binary instructions that a computer understands. No translation is
required.
Common errors
• Students often say that machine code needs translation.
• Students often reverse the definitions of high- and low-level languages.
Sample question
a) a Give one advantage of writing a program in a high-level language.
b) b Give one advantage of writing a program in assembly language.
c) c Give one advantage of writing a program in machine code.
Examiner's tip
Read the question carefully; does it ask for advantages or benefits or disadvantages or
limitations? Answer the question as set; both advantages and disadvantages require
a comparison. No comparison is required for benefits and limitations.
Student answer
a) Programs are easy to understand.
b) To make use of hardware.
c) Programs do not need to be translated.
Translators
In order to be used by a computer, programs need to be translated into the binary
instructions, machine code, that the computer understands.
Compilers
A compiler is a computer program that translates a program written in a high-level
language (HLL) into machine code so that it can be directly used by a computer to
perform a required task.
Interpreters
An interpreter is a computer program that reads a statement from a program written in
a high-level language performs the action specified and then does the same with the next
statement and so on.
Assemblers
An assembler is a computer program that translates a program written in an assembly
language into machine code so that it can be directly used by a computer to perform a
required task.
Summary
Complier
Interpreter
Assembler
Translates a high-level
language program into
machine code
Executes a high-level
language program one
statement at a time.
Translates a low-level
language program into
machine code.
An executable file of
machine code is produced.
No executable file of
machine code is produced.
An executable file of
machine code is produced.
One high-level language
statement can be
translated into several
machine code instructions.
One high-level language
program statement may
require several machine
code instructions to be
executed.
One low-level language
statement is usually
translated into one
machine code instruction.
Compiled programs are
used without the compiler.
Interpreted programs
cannot be used without the
interpreter.
Assembled programs can
be used without the
assembler,
A compiled program is
usually distributed for
general use.
An interpreter is often used An assembled program is
when a program is being
usually distributed for
developed.
general use.
Sample question
a) Describe two differences between a compiler and an interpreter.
b) State, with a reason, a situation where you would use each one. Each situation must
be different.
Student answer
a) A compiler translates a whole program at one go, an interpreter translates a line
at a time. A compiler produces a translated program, an interpreter does not.
b) Compiler: for distributing a program for general use, because the program will
not require the compiler to run.
Interpreter: for developing a program as errors are shown on a line by line basis.
Examiner's comments
In part a, the student has given two differences by explaining what happens in the same
situation in each case. For the first difference, it would have been more accurate to state
that the interpreter executes the program a line at a time.
In part b, the student has identified two different situations correctly. both reasons
given identify what is happening but not why it is useful. For the compiler, the users do
not have to download or purchase the compiler. For the interpreter, the developer can
resume the development of the program immediately one error has been corrected
without having to correct every error in the program.
Exam-style questions
1. Which translators are being described here?
a. 'translates a high-level language into machine codex
b. 'translates a low-level language into machine codex
c. 'executes a high-Level language program line by line'
[3 marks]
2. Identify the type of language that the following programs have been written in.
a) LDA
NoOne
ADD
NoTwo
STO'
Answer
b) Answer := NoOne + NoTwo
c) 1
4
0
d) 0001
0100
0000
12
13
1A
00010010
00010011
00011000
3. Name three different types of language translator and explain what each one is used
for.
4.
a) Give two disadvantages of writing a program in a high-level language.
b) Give two disadvantages of writing a program in a low-level language.