1. Computer Systems Nat 5 Computing Science
Translation of high-level program code to binary (machine code)

2. Lesson Aims By the end of this lesson:
All pupils will be able to describe:
A program
Machine Code
High Level Languages
Why High Level Languages require translation
How interpreters and compilers function

3. What is a program?
A set of instructions that a computer can understand
Programs are written in computer languages
The languages that we will learn about are:-
High-level languages
Machine code

4. Machine code The computer’s own language
Programs written in machine code just contain 1’s and 0’s
Difficult:-
for people to understand
To edit
To find errors
Machine code programs are each suited to a particular processor i.e. not portable

5. High level languages
Computer languages that use English words to write programs e.g. Visual Basic
Easy to:-
understand
edit
find errors
High Level Language programs can run on a variety of computers without being changed i.e. they are portable

6. Examples of High Level Languages
Use
Scratch
Learn to program
Visual Basic
COMAL
C++
Create applications, operating systems and games
HTML
Create web pages
JAVA
Internet programming

7. The need for translation
Nat 5
The need for translation
Computers only understand machine code
A translator program translates high-level languages programs into machine code
The machine code instructions can then be executed by the processor

8. How an interpreter works
Nat 5
How an interpreter works
Translates one line of the high-level language program into machine code then executes it
Translates the next line then executes it etc…
Translation takes place each time the programs is run

9. Features of interpreted programs
Error messages are reported as the program is developed
Interpreter must be in memory for the program to run
Program runs slow as translation takes place during execution

10. How a compiler works
Translates the entire high-level language program (source code) into a machine code program (object code)
The machine code (object code) program is saved and can be run without the need for it to be translated again

11. Features of compiled programs
Error messages only reported after the whole program has been compiled and object code produced
Compiler does not need to be in memory for the object code to run
Object code runs quickly as no translation is needed
Source code must be kept incase the program needs to be edited

12. Developing a program
An interpreter is usually used while a program is developed as the error reporting is useful
When the programs works it is compiled to produce a machine code program that is saved
It could be compiled a number of times to create machine code programs to suit a variety of processors – so it can be sold to more customers

13. A thought about efficiency…
For counter = 1 to 10
picOutput. Print “Hi”
Next
Interpreter – 30 lines of code are translated every time the program is run
Compiler – 3 lines are translated once and stored

14. Summary
Machine code:- understood by computers, contains only 1’s and 0’s
High-level languages:- use English words, easy to understand, must be translated
Interpreter:-
translates then executes a HLL line then translates and executes the next, etc
Program runs slowly and is translated each time it’s run. Interpreter must be in memory when program runs
Compiler:- translates source code into object code which is saved. Object code runs quickly without the compiler being in memory

15. Questions Name two high-level languages and state their uses.
What is a translator program?
Name two types of translator programs.
What is source code?
What is object code?

16. More questions Which translator program produces object code?
Which translator program must be in memory when the program is run?
Which type of translator is used if you want to create a program that runs fast?
Why must source code be kept after compilation?