Low-level languages

sit close to the computer's . An instruction set is the set of that the understands.

Two types of low-level language are:

Machine code

An instruction set relates to a specific processor and is written in machine code. The central processing unit (CPU) understands machine code directly and can act upon the instructions. A written in machine code consists of 0s and 1s only. Machine code is very difficult to learn, write and . Even a very simple program could have thousands of 0s and 1s in it.

Assembly language

Assembly language sits between machine code and in terms of ease of use. While high-level languages use to form instructions, assembly language uses (short abbreviations). Each mnemonic directly corresponds with a single machine code instruction. Here are some examples of mnemonics:

Mnemonic	Action
LDA	Loads a value from a memory address
STA	Stores a value in a memory address
ADD	Adds the value held in a memory address to the value held in the accumulator
SUB	Subtracts from the accumulator the value held in a memory address
MOV	Moves the contents of one memory address to another

Mnemonic	LDA
Action	Loads a value from a memory address

Mnemonic	STA
Action	Stores a value in a memory address

Mnemonic	ADD
Action	Adds the value held in a memory address to the value held in the accumulator

Mnemonic	SUB
Action	Subtracts from the accumulator the value held in a memory address

Mnemonic	MOV
Action	Moves the contents of one memory address to another

In assembly language, programmers write programs as a series of mnemonics. Mnemonics are much easier to understand and debug than machine code, giving programmers a simpler way of directly controlling a computer.

Assembly language is still used today, for example, in low-level embedded systems and device drivers. It is faster to run because it doesn’t need as much as a high-level language (see Translator section for more information).

Writing in mnemonics is easier for programmers because these abbreviations are usually brief representations of the actual commands. They are quicker to write than , and make it easier to spot mistakes.

‘Little Man Computer’ (LMC) is a simulation of a very basic processor using . It uses an example of assembly language that contains a limited set of mnemonic instructions which can be used to program simple assembly programs. ‘Little Man Computer’ is freely available on the internet for students to use.

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Programming languages - EdexcelLow-level languages