Paper 2

Does hexadecimal take up less space in a computer’s memory than binary

No, because it will still be represented using binary in a computer’s memory, so it will take up the same amount of memory space

What is the largest decimal number that can be represented using 5 bits

31

What is represented using binary

All data and instructions

Why is hexadecimal often used instead of binary

It’s easy for people to read, takes less time to type, more compact, reduces the risk of typing errors

How many bits does standard ASCII use for each character

7

How many different characters can be represented with standard ASCII

128

Advantages of UNICODE

Can represent a wider range of characters from other alphabets and more symbols

12KB in bits

96000b

Why do computers use binary

Computers are made from transistors with two states: on if a current is flowing through the component and off if it’s not, so it’s represented with either 1 or 0

Examples of bitmap image file formats (pixels)

PNG, JPG, GIF

Example of vector image file format (algorithms)

SVG

Pixel

A single point in an image

Image resolution

The concentration of pixels within a specific area

How to calculate image resolution

Width x height

PPI

Points per inch

DPI

Dots per inch

Colour/bit depth

Number of combinations

Bit depth to represent an image with 3 colours

2

Image file size in bits

image resolution x colour depth

Metadata

A set of data that describes and gives information about other data

ADC

Analogue to digital converter

DAC

Digital to audio converter

Amplitude

Height of a wave

How are soundwaves converted (5 bp)

Analogue sound is received by a microphone

Converted into an electrical analogue signal

The amplitude is measured at regular intervals (samples)

Values are rounded to a level (quantisation)

Values are stored as a series of binary numbers

Why does sound need to be converted to a digital format before it can be stored on a computer system

Sound is analogue and computers use discrete values

Sample resolution

Number of bits per sample

Advantage of a high sample resolution

Better sound quality

Disadvantages of a high sample resolution (2)

Takes up more storage space, will take longer to download

Sampling rate (unit)

Frequency with which you record the amplitude of a sound (Hz)

Hz

One sample per second

Sound file size in bits

Sampling rate x resolution x duration in seconds

Why is compression used (3)

Reduces the amount of storage to save files, uses less bandwidth (saves money), makes it faster to transmit

Lossy compression

Where files are compressed by permanently removing some of the detail

Disadvantage of lossy compression

Can decrease quality

Uses lossy compression

JPEG, MP3

Lossless compression

Reduces file size without losing any info

Why is lossless compression important

Essential for text and data files

Uses lossless compression

PNG, GIF

Feature needed for Run Length Encoding (RLE)

Lot of runs

Important things for huffman encoding

Characters with the lowest frequencies should be combined, table sorted by frequency

Hardware

The physical components that make up a computer system

Software

The programs that are stored and executed by a computer system (hardware)

System Software

Programs that provide a platform for other software to run on and manages computer systems

Application Software

Programs that enable a user to perform a specific task

Operating System (OS) Software

A group of programs that manages computer hardware, users, and the resources used by software

How does the OS manage processors?

It allocates where and for how long tasks/programs will run on the processors

Multi-Tasking

Where an OS manages simultaneous tasks

How does the OS manage memory?

It allocates and records where in the memory programs are stored

How does the OS manage input/output devices?

It controls the sending of data from the memory to the device driver

Device Driver (eg printers, monitors)

A program that controls peripheral devices

Interrupts

Signals sent to the CPU by external devices to indicate an event needs immediate action

How does the OS manage applications?

It runs programs to install applications and allows the user to interact with them

Graphical User Interface (GUI)

A visual system that allows users to interact with electronic devices

Application Programs Interface (API)

Allows applications to communicate with the OS

How does the OS manage security?

It keeps the computer system, application programs, and user data secure

User Management/ Access rights

Controls access to a computer by setting up passwords/different users with different privileges to files

What is encrypted for security management?

Hard drives and removable media

How does the OS protect the memory?

It prevents programs from overwriting eachother in the RAM

Utility Software

System software designed to help maintain, enhance, and troubleshoot a computer system

Disk defragmentation

Reorganises files so they are stored together to make them easier to access and optimises disk performance

Encryption software

Uses an algorithm and key to transform plaintext into ciphertext to keep sensitive data safe

Embedded system

A computer system with a specific function built into a physical device

Read Only Memory (ROM)

Non-volatile memory that can’t be changed

What are embedded systems used for?

Devices with simple inputs such as microwaves

Compression software

Reduces the size of a file

Low-level languages

A programming language that is closer to machine code and the hardware’s instructions

High-level languages

A programming language that is closer to human language, designed for ease of use, readability, and portability across different computer architectures

Processors

Can only execute instructions in machine code

Can you use machine code instructions on any device?

No, machine code instructions are specific to a particular processor

Machine code

The lowest-level programming language, specific to a processor, consisting of binary instructions that a computer’s CPU can directly execute

3 advantages of using a high level language

Easier for humans to debug as it’s closer to English, has data structures, portable between different hardware

2 disadvantages of using a high level language

Slower to execute, needs to be translated into machine code

2 advantages of low level languages

Faster and more efficient to execute, gives more control over specific hardware components

2 disadvantages of low level languages

Harder to read and write, not portable

Why might a programmer who can use high and low level languages use high level

Built in functions/libraries, data structure, easier to read and debug

What type of device is assembly language often used

Embedded systems

What does an assembler do?

Converts assembly language into machine code

How does a compiler work

It takes the source code and translates it all at once producing executable object code. It produces a list of syntax errors after translation

Why are compilers often used for copyright software

The end user can’t see the source code when the program is distributed and doesn’t need a compiler installed

How do interpreters work

Translates source code line by line and executes it immediately. If there is a syntax error it will stop

2 Disadvantages of using interpreters

End users can see the source code, interpreter software need to be installed

Which are faster, compilers or interpreters

Compilers

How does an assembler work

It translates all of the assembly code at once and outputs machine code. Users only need the compiled program

Central Processing Unit (CPU)

Processes and executes instructions

What is stored in the RAM?

Program instructions and data

Registers

Stores small amounts of data used when executing/processing instructions to be quickly accessed

Arithmetic Logic Unit (ALU)

Performs arithmetic, logical and shift operations

Control Unit (CU)

Controls and coordinates the execution of instructions by sending control signals, decodes instructions

Clock

Synchronises all CPU operations, controls the number of executed instructions per second, sends regular electronic pulses

Cache

Stores frequently used data and instructions in memory for fast access

Clock frequency (unit)

Number of clock cycles per second (Hz)

How does clock speed affect CPU performance

The greater the clock speed, the more FDE cycles/executed instructions per second, increasing peformacne

How does cache size affect CPU performance

Less need for the CPU to access the RAM (slower to access), improves the speed of performance, allows more data to be held

How does the number of processors affect CPU performance?

Allows more instructions to be executed simultaneously per second, different cores can deal with different types of instructions

Rank types of memory/storage by capacity (largest first)

Secondary storage, RAM, cache, registers

Buses

Used to transfer data/instructions between components in the CPU

Address bus

Stores the address of the memory/device controller location

Data bus

Carries data throughout the computer system

Control bus

Carries control signals (from the clock) to control all CPU activities

How is main memory used

It stores data/instructions whilst a program is being executed. Every memory location has a unique address so it can be found later when needed