Translators. Low level vs High Level Languages

OCR GCSE

(J277)

Teacher site: craigndave.org | Student site: student.craigndave.org | Smart revise: smartrevise.co.uk

SLR 2.5 Translators. High Level and Low level languages

Characteristics of compilers and

interpreters

Objectives

• Describe the characteristics and purpose of different

levels of programming language, including:

• Low-level languages

• High-level languages

• Understand the purpose of translators

• Describe the characteristics of a compiler

and interpreter

Translators and facilities of languages

Unit 8 Logic and languages

Starter

• Name five programming languages

• Are there any major differences between each of them?

Translators and facilities of languages

Unit 8 Logic and languages

Starter

• High-level Programming languages

• Python, Visual Basic, C#, Java, C++, PHP, Delphi, Logo

• Query languages

• SQL

• Markup languages

• HTML, XML

• Low-level Programming languages

• Assembly language, machine code

Translators and facilities of languages

Unit 8 Logic and languages

Machine code

• Computers were first invented in the 1940s

Translators and facilities of languages

Unit 8 Logic and languages

Machine code

• In the first computers, all programs were written in

machine code

• Instructions were written in binary, so a typical

instruction looked like this:

101011001001

• Each instruction did one very small task like

LOAD the value 1 into the accumulator

• Writing programs was difficult and time-consuming

Translators and facilities of languages

Unit 8 Logic and languages

Details of machine code are not needed.

You will not be asked to discuss assemblers or
compare them to other translators

But…you do need to know what a low level language
is

Using Assembly Language

What will this code do?
• LOAD 2
• SUB 3
• ADD #10
• STORE 4
• HALT

10

1

2

3

4

10

25

5

Using Assembly Language

What will this code do?
• LOAD 2
• SUB 3
• ADD #10
• STORE 4
• HALT

11

1

2

3

4

10

25

5

•

Loads the value 25

•

Subtracts the value 5 = 20

•

Adds on 10 = 30

•

Stores the answer (30) in
memory location 4

•

Stops the program

Translators and facilities of languages

Unit 8 Logic and languages

Assembly language

• Assembly language allows a programmer to create

programs more easily that writing in machine code

• Each assembly language instruction maps directly to

machine code

• For example:

LDA

51

ADD

#FF

STO

52

means “Load the contents of memory location 51 into the
accumulator, add hexadecimal value FF and store the result
in location 52”

1000101100000100001001010011001
1000000000000000000000000000001
01111111110000000000000000000000
0010001001000001000010010100110
10000000000

Machine code

Assembly language

Translators and facilities of languages

Unit 8 Logic and languages

Assembly language

• Assembly language is processor-specific

RISC – ASSEMBLY

CISC – ASSEMBLY

Translators and facilities of languages

Unit 8 Logic and languages

Assembly language

• It has to be translated into machine code before it

can be executed

• As each instruction corresponds directly to a

machine code instruction, it is known as a
low-level language (along with machine code)

Translators and facilities of languages

Unit 8 Logic and languages

Low-level advantages

• As a programmer has direct control over how a low-level program

works they have a number
of advantages, including:

• A program written in a low-level language can run very quickly

• The code will usually require less RAM

• Statements in a low-level language can be used to control and manipulate specific

hardware components

• As such, programs such as device drivers are often written in assembly

code

Open Ended

What is assembly code? How many machine code instructions does it get translated into

​Assembly code is a low level programming
language.
Each assembly instruction is translated into 1 machine code instruction

Translators and facilities of languages

Unit 8 Logic and languages

High-level languages

• High-level languages generally have statements that look a bit like

English or Maths

area = (base * height) / 2 print(area)

• This makes these

languages easier to
learn and understand
easy to learn
and understand

Translators and facilities of languages

Unit 8 Logic and languages

High-level languages

• High-level languages also have data structures such as arrays and

records

• A single statement usually translates into several machine

code instructions

• The translation is done by a program which may be either a compiler or

an interpreter

Open Ended

What is a high level language and what is the syntax of a high level language?How many lines of machine code is it translated into?

​High level programming languages read more like English or maths than assembly languages.

Each line typically is translated into many machine code instructions.

​High level programming languages read more like English or maths than assembly languages.

Each line typically is translated into many machine code instructions.

They have rules of grammar about how they are written called syntax.

Translators and facilities of languages

Unit 8 Logic and languages

TRANSLATORS

ASSEMBLY → MACHINE CODE (WHOLE PROGRAM)

COMPILERS → MACHINE CODE (WHOLE PROGRAM)

TRANSLATOR → MACHINE CODE (LINE BY LINE)

Translators and facilities of languages

Unit 8 Logic and languages

High level Languages (can be)
Machine independent

The Same C program

Different
Compiler for
RISC/CISC and/ or
UNIX/WINDOWS
32 bit vs 64 bit

Translators and facilities of languages

Unit 8 Logic and languages

High- and low-level languages

Translators and facilities of languages

Unit 8 Logic and languages

What do you think are advantages of high
level languages?

​•There are a number of advantages of high-level languages, including:

•A high-level language is easier to learn

•Programs can be written faster in a high-level language

•It is easier to understand and debug a high-level language

•Given all these advantages, why do you think that low-level languages are still used by
some programmers?

Translators and facilities of languages

Unit 8 Logic and languages

Given all these advantages, why do you think that
low-level languages are still used by
some programmers?

a) Some new CPUs (e.g. for an embedded device) may

not have a compiler written for them but will have an
assembler.

b) A very skilled assembly programmer can write more

efficient code than a compiler – so small often used
blocks of code could be rewritten and called from high
level language

Open Ended

What do you think are the advantages of high level languages (over low level languages)?

Translators and facilities of languages

Unit 8 Logic and languages

High-level Advantages

• There are a number of advantages of high-level languages, including:

• A high-level language is easier to learn and debug

• Programs can be written faster in a high-level language (as fewer lines of code)

• You can use data structures e.g. lists/records

• Given all these advantages, why do you think that low-level languages

are still used by
some programmers?

Open Ended

Given all these advantages, why do you think that low-level languages are still used by
some programmers?

Translators and facilities of languages

Unit 8 Logic and languages

Given all these advantages, why do you think that
low-level languages are still used by
some programmers?

a) Some new CPUs (e.g. for an embedded device) may

not have a compiler written for them but will have an
assembler.

b) A very skilled assembly programmer can write more

efficient code than a compiler – so small often used
blocks of code could be rewritten and called from high
level language

c) Can control specific hardware components, so are useful for device drivers (to control specific hardware elements of the peripheral device)

Translators and facilities of languages

Unit 8 Logic and languages

Worksheet 4

• Now complete Task 1 on Worksheet 4

Translators and facilities of languages

Unit 8 Logic and languages

Task 1

1. Insert the following languages into the correct column in the table:

Java, VB, Assembly code, Python, C++, machine code, C#, PHP

High-level language

Low-level language

Translators and facilities of languages

Unit 8 Logic and languages

ANSWERS

Translators and facilities of languages

Unit 8 Logic and languages

High-level language

Low-level language

Java

Assembly code

VB

Machine code

Python

C++

C#

PHP

Translators and facilities of languages

Unit 8 Logic and languages

True or False?

1.

A programming language which has statements
resembling English or Maths is classified as a
high-level language

True

2.

A high-level language is closer than a low-level
language to the machine code that the computer
can execute

False

3.
Assembly code does not have to be translated into
machine code before it can be executed
False

4.
An interpreter is a program that translates a high
level language into machine code
True

5.
A compiler is a program that translates a high
level language into machine code
True

6.
There are different assembly languages for
different processor types
True

7.
There are different high-level languages for
different processor types
False

Translators and facilities of languages

Unit 8 Logic and languages

Disadvantages of low-level code

True or False?

1.

An assembly program written for one type of
processor will not work on a different type of
processor

True

2.
Programs written in assembly will usually execute
faster than those written in a high-level language
True

3.

Low level languages cannot control individual
components in embedded systems such as those
found in washing machines or mobile phones

False

4.

Machine code produced from assembly language
will occupy more memory than the machine code
from a high level language

False

5.
Assembly language is harder to learn than a high
level language
True

Advantage

Translators and facilities of languages

Unit 8 Logic and languages

Compiler

• A compiler translates a high-level language into machine

code

• The code written by the programmer is called the source code

• The code produced by the compiler is called the object code

• The object code can be saved on a secondary storage drive

and run whenever required

Translators and facilities of languages

Unit 8 Logic and languages

Interpreter

• An interpreter is another type of program that

translates a high-level language into machine code

• Unlike a compiler, no object code is produced

• It translates each line of code and executes

it immediately

• If it reaches a line with a syntax error, it stops

and displays an error message

Translators and facilities of languages

Unit 8 Logic and languages

Picture round

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Low-level language

Assembly code

Machine

code

(Binary)

Translator
(Assembler)

High-level language

Source
code

Translator

(Interpreter)

Object
code

Translator
(Compiler)

Low-level assembly code is translated into machine
code using an assembler.

Object code is machine
code – the machine code for
some libraries may be
added later.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers

Code will not run while a syntax
error is present.

Here, we can see an error on
line 2 that is preventing our
program from running.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers

The error needs correcting
before the program will run.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Interpreters

This is exactly the same
program as the one we just
saw in Python – this time,
written in an early high-level
language called BBC Basic.

bbc.godbolt.org

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Interpreters

bbc.godbolt.org

When we run the program,
line 20 and line 30 are both
translated and run.

As you can see, it outputs
the value of counter here.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Interpreters

bbc.godbolt.org

It then tries to translate line
30 – however, there is a
syntax error on line 30, so
the program fails.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Interpreters

bbc.godbolt.org

Here, we can see that once
we correct the syntax error
on line 30 and run the
program again, it executes
without errors.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Compiler: Translates source code from high-level languages into object code and then into machine code
ready to be processed by the CPU. The whole program is translated into machine code before it is run.

Advantages:

•No need for translation software at runtime.

•Faster to execute.

•Code is usually optimised.

•Original source code can be kept secret.

Disadvantages:

•Source code is easier to write in a high-level language, but the program will not run with syntax errors,
which can make writing the code more difficult.

•Code needs to be recompiled following any changes.

•Designed for a specific type of processor.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Interpreter: Translates source code from high-level languages into machine code ready to be processed by
the CPU. The program is translated line by line as the program is running.

Advantages:

•Easy to write source code – the program will always run and only stop when it finds a syntax error.

•Code does not need to be recompiled following changes, making it is easier to try out commands.

•A very easy way for beginner programmers to learn how to write code.

Disadvantages:

•Translation software is required at runtime.

•Slower to execute.

•Code is not optimised.

•Source code must be available.

​Whiteboard Compilers vs Interpreters

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Compiler: Translates source code from high-level languages into object code and then into machine code
ready to be processed by the CPU. The whole program is translated into machine code before it is run.

Advantages:

•No need for translation software at runtime.

•Faster to execute.

•Code is usually optimised.

•Original source code can be kept secret.

Disadvantages:

•Source code is easier to write in a high-level language, but the program will not run with syntax errors,
which can make writing the code more difficult.

•Code needs to be recompiled following any changes.

•Designed for a specific type of processor.

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Interpreter: Translates source code from high-level languages into machine code ready to be processed by
the CPU. The program is translated line by line as the program is running.

Advantages:

•Easy to write source code – the program will always run and only stop when it finds a syntax error.

•Code does not need to be recompiled following changes, making it is easier to try out commands.

•A very easy way for beginner programmers to learn how to write code.

Disadvantages:

•Translation software is required at runtime.

•Slower to execute.

•Code is not optimised.

•Source code must be available.

Translators and facilities of languages

Unit 8 Logic and languages

Compiler or interpreter?

• Some languages, such as Java, are compiled into an intermediate

stage called bytecode

• The bytecode can be interpreted on many different types of

processor using an interpreter

• Javascript, used in creating web pages, is interpreted; the source code

is included in the web page and then interpreted in the browser (e.g.
Firefox, Chrome, Internet Explorer)

Open Ended

What are some advantages of interpreters over compilers?

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Interpreter: Translates source code from high-level languages into machine code ready to be processed by
the CPU. The program is translated line by line as the program is running.

Advantages:

•Easy to write source code – the program will always run and only stop when it finds a syntax error.

•Code does not need to be recompiled following changes, making it is easier to try out commands.

•A very easy way for beginner programmers to learn how to write code.

Disadvantages:

•Translation software is required at runtime.

•Slower to execute.

•Code is not optimised.

•Source code must be available.

​

Open Ended

What the advantages of compilers over interpreters?

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

Compilers and interpreters

Compiler: Translates source code from high-level languages into object code and then into machine code
ready to be processed by the CPU. The whole program is translated into machine code before it is run.

Advantages:

•No need for translation software at runtime.

•Faster to execute.

•Code is usually optimised.

•Original source code can be kept secret.

Disadvantages:

•Source code is easier to write in a high-level language, but the program will not run with syntax errors,
which can make writing the code more difficult.

•Code needs to be recompiled following any changes.

•Designed for a specific type of processor.

Translators and facilities of languages

Unit 8 Logic and languages

Interpretor advantages

Advantages:

•Easy to write source code – the program will always run and only
stop when it finds a syntax error.

•Code does not need to be recompiled following changes, making
it is easier to try out commands – note big programs can take
hours to compile.

•Machine independence - Source code can sold – as long as
machine has its own interpreter then this can run. In compiled
languages many versions for each machine type (OS + CPU)
must be compiled and correct one installed

•A very easy way for beginner programmers to learn how to write
code.

​

Open Ended

Describe as many features of low level languages as you can

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

High- and low-level languages

Machine code

• Binary representation of instructions in a format that the CPU can decode

and execute.

• Includes an operation code (opcode) instruction and address or data to use

(operand).

Low-level languages

• Written in assembly language.
• Converted into machine code using a translator called an assembler.
• Used for embedded systems and device drivers where it is necessary to

instruct hardware directly.

• One instruction translates into one machine code instruction.
• Code only works with one specific type of processor.
• Programmers work with memory directly.
• Code is harder to write and understand.
• Memory-efficient.
• Code is quick to execute.

Open Ended

Describe as many features of high level languages as you can

OCR GCSE (J277)

SLR2.5 Programming languages and IDEs | Characteristics and purpose of different levels of programming language

High- and low-level languages

High-level languages

• Written in languages like Python, C++, Java and Visual Basic.
• Converted into machine code using a translator called a compiler or

interpreter.

• Makes writing programs easier by utilising commands that are like

English.

• One source code instruction translates to many machine code

instructions.

• Code will run on different types of processors.
• Programmers can use many different data structures.
• Code is quicker and easier to understand and write.
• Less memory-efficient.
• Code can be slower to execute if it is not optimised.

Translators and facilities of languages

Unit 8 Logic and languages

Worksheet 4

• Now complete Task 2 on Worksheet 4

Translators and facilities of languages

Unit 8 Logic and languages

Task 2
The Python code below contains a syntax error and a logic error.
1

# Program to perform a bubble sort

2
3

userName = ["Carl","Tamsin","Eric","Zoe","Alan","Mark"]

4

print("list of unsorted names: ", userName)

5

#numItems is the length of the list

6
7

while numItems > 1:

8

for count in range(5):

9

if userName[count] > userName[count + 1]:

10

temp = userName[count + 1]

11

userName[count] = userName[count + 1]

12

userName[count + 1] = temp

13

prnt("count = ",count, "userName[count] = ",~

userName[count], "userName[count+1] ="
,userName[count+1])

14

numItems = numItems – 1

15

prnt(userName)

(a)

There is a syntax error in line 15. What is the error?

Translators and facilities of languages

Unit 8 Logic and languages

(b)

Python programs are interpreted.

What, if anything will be printed when the program is run? (after corrected)

(c) If you have Python installed on your computer, try out the code and see if you are

right.

(d)If numItems = 6 is now inserted at line 6, what will happen when the program is

run?

(e)When this error is fixed, does the program give the correct result? If not,

correct it.

Translators and facilities of languages

Unit 8 Logic and languages

(a)

There is a syntax error in line 15. What is the error?

The print statement has been spelt incorrectly

(b)

Python programs are interpreted.

What, if anything will be printed when the program is run?

The interpreter ignores the comment on line 1, translates lines 2 and 3 and prints
the list at line 4. It then crashes on line 7 because numItems is not defined.

list of unsorted names: ['Carl', 'Tamsin', 'Eric', 'Zoe',
'Alan', 'Mark']
Traceback (most recent call last):

File "C:\W4 bubble sort, line 7, in <module>

while numItems > 1:

NameError: name 'numItems' is not defined

.

Translators and facilities of languages

Unit 8 Logic and languages

(c) If you have Python installed on your computer, try out the code and see if you are

right.

(d)If numItems = 6 is now inserted at line 6, what will happen when the program is

run?

The program will run to line 18, where it stops with the error message

Traceback (most recent call last):

File "C:\W4 bubble sort, line 18, in <module>

prnt (userName)

NameError: name 'prnt' is not defined

(e)When this error is fixed, does the program give the correct result? If not, correct it.

change temp = userName[count + 1] to

temp = userName[count]

See program W4 Bubble sort.py. This program was given in the lesson on Errors
and testing so most students should already have found the logic error.

​Complete . Then ask students for each word

Translators and facilities of languages

Unit 8 Logic and languages

Plenary

• Complete the following by filling in the blanks

High-level languages include Python, VB and Java. They need to be
compiled or interpreted before they can be run. Assembly language is a
low-level language. It is assembled into machine code before it is run.

Compiled

Assembly language

Machine code

Python

High-level

assembled