Computing EOY

Input device

Gets data from real world (e.g. mouse and keyboard) and converts it into form that can be stored on computers

Output device

When input is processed and the computer system generates outputs (e.g. speaker)

Von Neumann Architecture

Used idea of holding both programs and data in memory. Data would then move between the memory unit and the processor

CPU

Central processing unit - hardware that executes programs and manages rest of hardware (brain of the computer)

Cache memory

Very fast memory, close to the CPU, used to temporarily hold data or instructions that are likely to be needed again by the processor in the program

Fetch-Decode-Execute Cycle

Fetch instruction from main memory (where program is first loaded), decode the instruction and execute it

What does the CPU contain?

Control Unit, ALU and registers

Control Unit

Coordinates all activities taking place inside the CPU. Controls execution in correct sequence, decodes instructions, regulates processor timing using pulses from system clock and sends and receives control signals to and from other devices within computer

ALU

Arithmetic and Logic Unit - Carries out Logical Operations (AND, OR, NOT), Shift Operations (bits in computer are shifted left or right) and Arithmetic Operations

Register

Special, very fast memory location within the CPU used in the execution of instructions

Special-purpose Registers in CPU

MAR, MDR, PC and ACC

Register - MAR

Memory Address Register - holds the address of the instruction or piece of data to be fetched or stored

Register - MDR

Memory Data Register - holds data or program instruction temporarily when it is fetched from memory or is being sent to memory

Register - PC

Program Counter - holds the memory address of the next instruction to be processed

Register - ACC

Accumulator - Memory location which results of operations carried out in ALU are temporarily stored

Factors affecting CPU performance

Clock speed, Cache size, Number of cores

Clock speed

Speed at which a processor operates (measured in hertz)

How does the clock speed affect CPU performance

Faster clock means more instructions are fetched, decoded and executed in a given time

Bottleneck

When other components contribute to overall speed in the computer that leads to a bottleneck and causes system to slow down

How does cache size affect performance of CPU?

Cache memory makes any data frequently used by the CPU much more quickly and because the processor has to access main memory less frequently (which is slower), it can work faster, so CPU performance increases - more cache means more data can be held in cache and make data available quickly

Level 1 cache

Extremely fast but very small (2-64KB) hence speeding up fetch-decode-execute cycle

Level 2 cache

Faster than RAM and medium sized (256KB-2MB)

Number of Cores

Tells you how many processing units are within the CPU (meaning parallel processing can take place)

How does the number of cores affect CPU performance?

More CPU cores increase performance by allowing a computer to handle multiple tasks simultaneously, significantly enhancing multitasking, rendering, and heavy application performance

Why doesn’t having more cores always mean higher CPU performance?

Many applications are not designed to use multiple cores efficiently, meaning they cannot be parallelised and tasks often run in sequence, requiring cores to wait for others, and communication between cores can limit speed.

Embedded System

Small computer built into a piece of equipment designed to perform a specific function

RAM

Random Access Memory - Type of memory used as the computer’s main memory, acts as temporary storage for programs and data while the program is being executed

Need for primary storage

Very fast access speeds - how quickly can we read from and write from to a device

Primary storage

Consists of RAM, ROM, registers and cache - holds data that the CPU needs to access while computer is running

What is virtual memory?

Virtual memory is part of secondary storage used as extra RAM when the computer runs out of main memory.

Why is virtual memory needed?

To allow more programs to run when RAM is full.

Where is virtual memory stored?

On secondary storage (hard drive or SSD).

How does virtual memory work?

The OS moves inactive data from RAM to secondary storage, freeing up RAM for active processes.

What happens when data in virtual memory is needed again?

It is transferred back into RAM.

What is a disadvantage of virtual memory?

It is slower than RAM, so it reduces system performance.

What is “thrashing”?

When the system spends too much time swapping data between RAM and virtual memory, causing major slowdowns.

ROM

Read-Only Memory - you cannot write over the contents once it has been created (type of primary strorage)

Is ROM volatile or non-volatile?

Non-volatile

Volatility

When you turn off the computer it loses its contents

Is RAM volatile or non-volatile?

Volatile

Characteristics of RAM

Volatile, stores user data of OS which is currently in use and memory can be written to or read from

Boostrap loader

Small program that loads the operating system

Characteristics of ROM

Non-volatile, used to store bootstrap loader and memory can only be read from and not written to

Secondary storage

Non-volatile, holds much more data than main memory but have slower access speeds

Features to choose secondary storage

Capacity (how much space), speed, portability (how easy to carry), durability (how easily it’s damaged), reliability (how long it lasts) and cost

Secondary storage - Magnetic devices

Read with a moving head inside the disk drive (moving makes it slow and susceptible to damage) - can either be internal or portable (connected to the computer using USB port)

Solid State Drives

SSD - no moving parts and don’t rely on magnetic fields

Use of internal Hard disk

inside a PC as secondary storage

Use of portable Hard disk

Supplementary storage for a PC or portable storage where high capacity is required

Benefits of SSD over HDD

More reliable (less damage - no moving parts)
Lighter (suitable for modern devices)
Faster access time (don’t have to wait for head to spin)
Lower power consumption
Run much cooler than HDDs
Can be very thin

Types of SSDs

Internal Solid state, USB memory stick, memory card

Use of internal solid state

PCs, notebooks, tablets and laptops

How reliable are internal solid state

Extremely reliable

Uses of USB Memory Stick

Personal use - moving files between computers

Uses of memory cards

In phones and cameras

Reliability of USB Memory Stick

Very reliable but can corrupt files if removed from PC too soon

Reliability of Memory Card

Very reliable

Types of Optical devices

CD, DVD and Blu-Ray discs

Optical devices

Have moving parts, which makes transfer speeds and access times relatively slow compared to SSD

Why do we use binary?

Computers have millions of transistors which can only go on (1) or off (0), so for them to understand, we use the base-2 system

Bit

1 or 0

Byte

8 bits

Kilobytes

1000 bytes

Megabyte

10^6 bytes

Gigabyte

10^9 bytes

Terabyte

10^12 bytes

Petabyte

10^15 bytes

Binary addition - 0+0

0

Binary addition - 0+1 or 1+0

1

Binary addition - 1+1

0 carry 1

Binary addition - 1+1+1

1 carry 1

Binary shift

Shifting left multiplies by 2 and shifting to the right divides by 2

Overflow error

Where binary value is too big to store in bits available so outcome results in overflow error

Hexadecimal

Base-16 system - A=10, B =11 etc…

Nibble

4 bits

Why do technicians use hexadecimal?

Because it acts as a human-friendly bridge between compact human-readable text and the long strings of binary (0s and 1s) that computers actually understand.

ASCII

Character set - each letter is assigned a set of binary digits

Character set

Logically ordered set of all the characters that can be encoded using a given number of bits

How many bits per character does ASCII use?

7 bits for each character. Extended ASCII uses 8 bits for each character (gives additional 128 characters in total)

Character set - Unicode

New standard for representing the characters of all the languages of the world

Resolution of an Image

Measured in Pixels Per Inch (PPI) and is the measure of the quality of the images - number of pixels in an image

Colour depth

Bits per pixel - calculate minimum required depth by doing 2^number of colours

File size for an image

Image width x Image Height x colour depth

Metadata

“data about data” - e.g. type of file, time and date of creation, creator or author of data, file size

Analogue

Continuously changing (sound waves are analogue)

ADC

Analogue to Digitial Converter - takes real-world analogue signals and converts them to a digital representation

Sample

Measure of amplitude at one point in time - more often you take this, the smoother the playback will sound

Sample resolution

Number of bits used to store each sample

Sample rate

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

Sample size

Number of seconds over which the sample was taken

File size of a sound file

Sample rate x sample resolution x seconds

Why is compression used

To reduce amount of storage needed on a computer to save files, allow large files to be transmitted as an email attachment and to allow a file to be transmitted in less time

Lossy compression

Where files are compressed by removing bits of detail (used to compress images, audio files and video files where it is easier to recognise even if some data is missing)

Lossless compression

Where files are compressed but no data is lost (e.g. for text and data files)

Internet

Worldwide connection of inter-connected networks, not owned or managed by any one group of people

World Wide Web

All information on WWW is stored in web pages. These can be accessed using a web browser

IP addressing

Every networked computer has a unique IP address

IPv4

Takes the form of 1-256 number separated by dots (e.g. 123.123.123.123)

IPv6

128 bits long (4 times length of IPv4) arranged in eight groups of 16-bits each separated by colons (each group is 4 hexadecimal digits)

What does IP stand for?

Internet Protocol