Unit 1: History of Programming

Question 1

Machine code

Answer 1

A form of digital (binary) information that is processed by and determines the actions performed by a computer’s Central Processing Unit (CPU).

The code is normally stored as a sequence of bytes in memory, and the fundamental functionality of a CPU is to execute this code as a sequence of instructions.

Question 2

3 Actions resulting from machine code instructions

Answer 2

• Logical and arithmetic manipulation of digital data
• Transfer of data from one memory location to another
• Making the sequence of execution jump to a new memory location

Question 3

How many registers does a Z80 CPU have?

Answer 3

8 main registers designated
A, B, C, D, E, F, H, L

Question 4

How much information can a Z80 register store?

Answer 4

8 Binary Bytes

Question 5

4 Kinds of operations that can be performed by a Z80 CPU

Answer 5

• Load a byte into a register
• Copy bytes from one register to another
• Copy bytes from a register to a memory location or vice versa
• Perform arithmetic operations on register contents.

Question 6

Low-level programming language

Answer 6

A programming language that provides little or no abstraction from a computer’s instruction set architecture.

Generally this refers to either machine code or assembly language.

Question 7

Instruction set

Answer 7

A set of instructions that the processor understands.

Question 8

Machine code

Answer 8

The set of instructions that a CPU understands directly and can act upon.

A program written in machine code would consist only of binary.

Question 9

Assembly language

Answer 9

Sits between machine code and high-level language in terms of ease of use.

While high-level languages use statements to form instructions, assembly language uses mnemonics - short abbreviations.

Each mnemonic directly corresponds with a machine code instruction.

Question 10

Give 5 examples of Assembly mnemonics

Answer 10

LDA, STA, ADD, SUB, MOV

Question 11

LDA Mnemonic

Answer 11

Loads a value from a memory address

Question 12

STA Mnemonic

Answer 12

Stores a value in a memory address

Question 13

ADD Mnemonic

Answer 13

Adds the value held in a memory address to the value held in the accumulator

Question 14

SUB Mnemonic

Answer 14

Subtracts from the accumulator the value held in a memory address

Question 15

MOV Mnemonic

Answer 15

Moves the contents of one memory address to another.

Question 16

Von Neumann architecture

Answer 16

A description of the processing architecture that all CPUs use.

John von Neumann invented the processor architecture which stores a program in memory as instructions and executes them sequentially using the ALU, control unit, and registers.

This is known as a stored program concept.

Question 17

2 Parts to machine code and assembly instructions

Answer 17

• The opcode
• The operand

Question 18

Opcode

Answer 18

Operation code.

Specifies instructions that can be executed by a CPU / processor in machine code.

E.g. in an instruction like “move the value 3 to the memory address X”, the opcode is move.

Question 19

Operand

Answer 19

Data that is manipulated by the CPU/processor according to the given opcode.

E.g. in the instruction “ADD 3”, the operand is 3.

Question 20

Assembler

Answer 20

A program that translates assembly languages into machine code.

Question 21

Binary

Answer 21

A number system that contains two symbols, 0 and 1.

Also known as base 2.

Question 22

Compilation

Answer 22

The process of translating source code into object code all in one go.

The program can then be executed as a whole.

Question 23

Compiler

Answer 23

A program that translates high-level programming languages into machine code.

Question 24

Denary

Answer 24

The number system that is most commonly used by people.

It contains 10 unique digits 0 to 9. Also known as decimal or base 10.

Question 25

Hexadecimal

Answer 25

A number system using 16 symbols from 0-9 and A-F, also known as base 16 and hex.

Question 26

Translator

Answer 26

Program translators convert program code into machine code to be executed by the CPU.

Question 27

3 Types of translators

Answer 27

• Interpreter
• Compiler
• Assembler

Question 28

Church-Turing thesis

Answer 28

A function on the natural numbers can be calculated by an effective method if and only if it is computable by a Turing machine.

All programming languages capable of certain fundamental processing capabilities are equivalent to Turing machines, and so have essentially the same computing power (they can perform the same calculations).

Question 29

Source code

Answer 29

A set of instructions that are written in human-readable programming language.

Source code must be translated into machine code before a computer can understand and execute it.

Question 30

3 Advantages of compilers

Answer 30

• Compiled programs run quickly since they have already been translated.
• A compiled program can be supplied as an executable file (ready to run).
• Compilers optimise code. Optimised code can run quicker and take up less memory space.

Question 31

2 Disadvantages of compilers

Answer 31

• Source code must be re-compiled every time the programmer changes the program.
• Source code compiled on one platform will not run on another - the machine code is specific to the processor’s architecture.

Question 32

Interpreter

Answer 32

Translates source code into machine code one instruction at a time.

The resulting machine code is then executed immediately.

Question 33

2 Advantages of interpreters

Answer 33

• Instructions are executed as soon as they are translated.
• Errors can be quickly spotted - once an error is found, the program stops running and the user is notified at which part of the program the interpretation has failed. This makes interpreters extremely useful when developing programs.

Question 34

4 Disadvantages of interpreters

Answer 34

• Interpreted programs run slowly as the processor has to wait for each instruction to be translated before it can be executed.
• The program has to be translated every time it is run.
• Interpreters do not produce an executable file that can be distributed. As a result, the source code program has to be supplied, and this could be modified without permission.
• Interpreters do not optimise code - the translated code is executed as it is.