Low-level Languages — Programming Languages and Translators | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 4% of your exam marks.

stable

Rare

Stable4%

Compiler vs interpreter differences are a recurring 3-mark question.

A is one where each instruction maps directly or very closely to a single machine-code instruction, and where the programmer has direct control over the computer's hardware (registers, memory addresses, processor instructions).

There are two low-level languages to know: and .

Machine code (1st generation)

Machine code is the raw binary language the CPU runs directly. Every instruction is a string of 1s and 0s that matches one specific operation in the CPU's instruction set.

A machine-code instruction might look like 10110111 00000101, which is meaningless to a human reader, but the CPU can execute it without any translation step.

Directly executed by the processor.
Specific to one CPU architecture. Machine code for an Intel x86 chip will not run on an ARM chip.
Almost impossible to write by hand for any non-trivial program.

Assembly language (2nd generation)

Assembly language is a low-level language where each binary machine-code instruction is replaced with a short, human-readable abbreviation called a .

Typical assembly mnemonics:

Mnemonic	Meaning
LDA	Load: copy a value from memory into the accumulator
STA	Store: copy the accumulator's value into a memory location
ADD	Add a value to the accumulator
SUB	Subtract a value from the accumulator
JMP	Jump to a different instruction

Assembly is far easier for humans to write than raw machine code, but it is still one-to-one with machine code: each assembly instruction translates to exactly one machine-code instruction.

Before assembly can run, it must be translated into machine code by a piece of software called an (covered in section 4).

Why use a low-level language?

Modern programmers rarely write entire programs in assembly, but low-level code is still used for specific situations:

When direct hardware control is needed (writing a device driver, programming a microcontroller, talking to specific CPU registers).
When maximum speed is needed in a small section of code (game engines, signal processing).
When memory is very tight (embedded systems, boot loaders, small microcontrollers).
When the code is specific to a particular CPU anyway, so machine dependence is not a problem.

Advantages and disadvantages of low-level languages

Advantages	Disadvantages
Direct control of memory, registers and hardware	Hard to read and write for humans
Efficient: small memory footprint, very fast execution	Machine-dependent: code only runs on one CPU architecture
Predictable timing (useful in real-time systems)	Easy to make mistakes that crash the system
	Slow to develop compared to high-level languages

Exam tip

Giving a benefit of using a low-level language

What comes up: A question asks for one advantage of writing code in a low-level language (assembly) rather than a high-level language.

Write: Any one of: (1) the programmer has direct control over the hardware (registers, memory addresses); (2) the code executes faster and uses less memory; (3) the programmer can use processor-specific instructions that are not available in a high-level language.

Watch out: Saying the code "does not need to be translated" is only partly true for assembly (it still needs an assembler); machine code alone needs no translation. Keep your answer precise about which level you mean.