key words

Purpose of the CPU

To process data and instructions, and to fetch and execute instructions

What is the ALU?

Arithmetic logic unit, component of CPU that performs arithmetic/logical operations

What is the control unit?

The control unit sends control signals to direct the operation of the CPU.

It decodes instructions as part of the F-E cycle

What is a register?

A register is a temporary storage space for one instruction or address

What is cache memory?

It is used to temporarily hold instructions and data that the CPU is likely to reuse.

Slower to access than registers but faster than RAM

What is Von Neumann architecture?

A computer with VNA stores both program instruuctions and data in the same memory (RAM).

Data is transferred between components on pathways called buses

What is the program counter?

tracks the RAM address of the next instruction to be fetched

What is the memory address register?

tracks RAM address of the instruction that is to be fetched

What is the memory data register?

Stores instructions that has been transferred from RAM to CPU

What is the Current Instruction Register?

Stores instruction that has been fetched from RAM, and is about to be decoded or executed

What is the accumulator?

Stores the result of mathematical or logical calculations.

Fetch - Execute Cycle

1. The Program Counter (PC) register displays the address in RAM of the next instruction to be processed.

This value is copied into the Memory Address Register (MAR).

0054

2. The PC register is increased by 1.

This prepares the CPU for the next instruction to be fetched.

0055

3. The CPU checks the address in RAM which matches the address held in the MAR.

0054

4. The instruction in RAM is transferred to the Memory Data Register (MDR).

5. The instruction in the MDR is copied into the Current Instruction Register (CIR).

6. The instruction in the CIR is decoded (understood) and executed (processed).

Any result of an execution is stored in the Accumulator (ACC) register.

7. The cycle repeats by returning to the first step and checking the program counter for the address of the next instruction.

How does cache size affect the performance of the CPU?

Cache memory is closer the the CPU than RAM meaning it can provide data and instructions to the CPU faster.

More cache memory = higher performance because repeatedly used instructions can be stored and accessed faster

Disadvantage of cache memory?

Costly so most computers have a small amount

What is clock speed?

It is how quickly a CPU can process instructions (Hertz) 3.5 Ghz = 3.5 billion cycles a second

How does clock speed affect CPU performance?

The higher the clock speed, the greater the number of fetch-decode-execute cycles a core can carry out per second resulting in better performance.

What is overclocking and underclocking?

Overclocking is when clock speed is increased higher than recommended. Leads to overheating and damage of machine

Underclocking is when clock speed is decreased lower than recommended. Increases lifespan of computer

What is the core?

A 'core' is a complete processing unit within the CPU - it has an ALU, Control Unit and Registers

How does the number of cores improve performance?

More cores = more instructions being processed at once

What are disadvantages of having more cores?

if one core is waiting for another core, performance may not increase at all.

Some software is not written to make use of multiple cores, wont run any quicker

What is an embedded system?

A computer system built into a larger machine to provide a means of control.

They perform specific pre programmed tasks which are stored in ROM

Hardware and Software

Examples of Embedded Systems

Washing Machine, Digital Camera and Microwave oven.

Primary Storage

Very quick because it is directly accessed by CPU

Smaller in storage

RAM and ROM

Secondary Storage

Slower as it isn’t directly accessed by CPU

Larger storage

Long term storage

Magnetic, Optical and Solid State

What is volatile memory?

Storage that is wiped clean when power is cut off from a device. RAM

What is non-volatile memory?

Non-volatile memory is memory that keeps its information after the power supply is cut. ROM

What is RAM?

RAM is volatile storage that stores all programs that are currently running.

Made up of a large number of storage locations, identified by unique address.

What is ROM?

Read Only Memory

Non volatile storage that stores the boot program/BIOS.

Bios loads up operating system

What is virtual memory?

a portion of the hard disk designated to function as additional RAM

Magnetic Storage

Hard drives

ADV: fast access, stores large amounts of data, low cost

DIS: not very portable, easily be broken

Optical Storage

CD, DVD, Blu-Ray

ADV: thin, portable and cheap

DIS: Slowest access speed, low capacity, not durable

Solid State Storage

SSDs, USB stick, Memory card

ADV: Durable but USB sticks can be broken, portable because small,

Fastest access speed

What is all data in a computer made up of?

Bits which can either be a 0 or 1

What is 4 bits?

1 nibble

What is 8 bits?

byte

What is 1000 bytes

1 kilobyte

What is 1000 kilobytes (KB)?

1 Megabyte (MB)

What is 1000 Megabytes

1 gigabyte

What is 1000 Gigabytes

1 terabyte

what is 1000 terabytes

1 petabyte

Why do computers use binary?

Computers only understand electricity on and electricity off; 1 represents electricity on whereas 0 represents electricity off.

What is denary?

Denary is a base 10 number system with 10 digits 0-9

How to convert binary - denary

use 1 2 4 8 16 32 64 128 in a table and write down the binary under.

add the numbers with a 1 underneath.

How to convert denary - binary

Use a table with up to 128

if target number (i.e 178) is larger than place value (i.e 128) we write a 1. If it is less we write 0

How to add binary numbers?

0 + 0 = 0

1 + 0 = 1

1 + 1 = 0 (carry 1)

1 + 1 + 1 = 1 (carry 1)

What is an overflow error?

When the result of a binary calculation is too long for a computer to process

How to convert binary - hexadecimal

split binary number in half

8 4 2 1 table

add numbers with 1 underneath

if more than 10, 10A - 15F

if less than 10, 1-9

1101011 is D7

How to convert hexadecimal - binary

example question 5B to binary

use 8 4 2 1 table

left nibble needs to make five so left is 0101

right nibble needs to be B (11) so right is 1011

Convert denary to hexadecimal

convert to binary then hexadecimal

or

convert to binary then denary

what is binary shift?

Moving the bits in a binary number left or right and filling the gaps at the beginning or end with 0s

What is a character set?

A representation of characters as numbers. Each character gets a number. Unicode and ASCII are character sets.

What is ASCII?

7 bit code that can hold 128 characters

What is Unicode?

Unicode is used for internal representation of characters and strings and it uses 16 bits to represent each other.

How to calculate file size of a text file?

bits per character x number of characters

What are bitmap images?

Images that are composed of small dots called pixels.

Each pixel is assigned a binary value which represents the colour of pixel

What is image resolution?

number of pixels in image

What are vector images?

Vector images are drawn by computers following precise mathematical instructions to create lines and objects

How to calculate file size of a bitmap?

Resolution x colour depth

Metadata

Additional data about a file.

Height in pixels

Width

Colour depth

Resolution

How to sample an analogue sound wave?

To get highest quality sound, many samples are taken to recreate the analogue wave as closely as possible

What is sample rate?

Number of times the amplitude of the sound wave is measured

How does sample rate affect quality of sound?

Low sample rate = low quality because digital data doesnt closely resemble original analog wave

High sample rate = high quality because digital data closely resembles analog wave

How does bit depth affect sound quality?

The higher the bit depth, the more bits available to represent each sample.

Calculating sound file sizes

File size (bits) = sample rate x bit depth x duration

Benefits of compression

Less storage space used

Files can be uploaded and downloaded quicker

Limits of streaming service can be avoided

What is lossy compression?

Compression in which some of the information is permanently eliminated

What is lossless compression?

Compression in which all the original data can be recovered when the file is decompressed

What is a LAN?

Local Area Network - a network that connects computers within a limited area such as a school or office

What is a WAN?

Wide Area Network; uses long-range telecommunication, links across country or continent

What factors affect performance speed?

Bandwidth available

Users using at same time

Thick walls

Distance

client/server network

A client makes requests to the server, the server manages the request and responds.

Advantages of a client-server network

-Sharing devices (e.g. printers) saves money.

-Site software licenses are likely to be cheaper than several standalone.

-Files easily be shared between users.

-Good security, users cannot see other users' files (unlike on stand-alone machines)

-Data is easy to backup as stored on the file server

Disadvantages of client server network

- Network cabling and file servers can be expensive.

-Professional IT staff needed to maintain servers and run network

-If file server breaks down the files become inaccessible.

-Viruses easily spread to other computers in network.

-Danger of hacking, particularly WANs. Security protocols needed to prevent it

peer-to-peer network

Data is shared directly between systems without requiring a central server

peer-to-peer network advantages

Easy to implement, inexpensive, no servers

peer-to-peer network disadvantages

Less security

Prone to viruses

The more people, the worse it will perform

Star Topology Advantages

-One cable or computer failing doesn't affect any other computers.

-Very few data collisions as each computer has its own cable to connect to the server so data travels quickly.

-New computers can be added to the network without

disrupting the other computers.

-New computers can be added with little affect on the speed that data travels round the network.

Star Topology Disadvantages

the whole network fails if the switch fails as no node can communicate

a wired star topology requires plenty of cable - in a large network this can be expensive

Mesh Topology Advantages

new nodes can be added without interruption or interfering with other nodes

multiple connections mean each node can transmit to and receive from more than one node at the same time

messages should always get through as they have many possible routes on which to travel

Mesh topology disadvantages

Lots of cable. Installation and re connection difficult. Too much equipment. Expensive

wireless access point

Provides a link between wireless and wired networks. Creates a wireless local are network that allows WiFi enabled devices to connect to a wired network

Router

A type of computer that forwards data across a network

Receive data packets and use the IP address in packet header to determine best route to transmit data

Switches

Used to connect devices together on a LAN

Receives data packets from a connected node, reads the destination address in packet header and forwards data directly to its destination.

Network Interface Card (NIC)

Internal piece of hardware that is required for the computer to connect to a network

transmission media

Ethernet cables

Fibre optic cables

Coaxial cables

DNS server

stores a list of domain names and a list of corresponding IP addresses where the website is stored

Steps taken to display web page

1. Domain name is typed into browser

2. Query is sent to the local DNS server for the corresponding IP address of the domain name.

3. DNS server checks if it holds an IP address corresponding to that domain name. If it does, it passes IP to your browser.

4. Browser then connects to the IP address of the server and accesses website

What is cloud storage?

a place to save your files and access anywhere with an internet connection

Cloud storage advantages

It can offer additional storage for needs (business or personal)

Very efficient method of backing up data and so saves time and money

Allows employees to work from anywhere i.e. work from home, when travelling via mobile devices

Environmentally friendly

Don't need specialist network skills - save more on staff

The third party provides security so saves money on staff and software/hardware

Wired connections

• Ethernet cable - Direct connection

• Fastest connection is the default - Ethernet, Wireless, WWAN

• Alternate configurations - Use when DHCP isn't available

wireless connections

Connecting devices to the internet or other devices without the use of wires.

Wifi or Bluetooth

SLOWER

LESS SECURE

FREEDOM OF MOVEMENT

TCP/IP

TCP allows packets to be sent and received between computer systems. Breaks data packets and reassembles them back at the destination.

IP is in charge of routing and addressing data packets. Ensures they are sent to the correct destination.

HTTP/HTTPS

HyperText Transfer Protocol - the protocol used for transmitting web pages over the Internet

HyperText Transfer Protocol Secure - more secure version as it uses ssl

FTP (File Transfer Protocol)

A protocol used to transfer files across a network.

SMTP (Simple Mail Transfer Protocol)

Used to send emails to mail servers and between mail servers

POP (Post Office Protocol)

receives and stores emails from a mail server. POP deletes an email from the email server.

IMAP (Internet Message Access Protocol)

a common protocol for retrieving and storing emails from a mail server. Syncs message with an email server so it can be accessed by different devices

IP vs MAC address

IPv4 uses a 32-bit address that allows for over 4 billion unique addresses.

IPv6 - was developed with a 128-bit address, represented in hexadecimal

A MAC address is a unique hexadecimal number assigned to each network interface card inside a networked device e.g. a router or a laptop.

While an IP address may change, the MAC address can't be changed.

4 layer TCP/IP model

Application- Allows humans and software applications to use the network e.g. browsers (HTTP/HTTPS) and email (SMTP) and file transfer (FTP).

Transport- TCP breaks the data down into data packets. This layer makes sure the data is sent and received in the correct order and reassembled at the destination without errors.

Network- IP is responsible for addressing and routing data packets. The optimal route for the data to take is calculated in this layer.

Also known as the 'Internet Layer'.

Data Link- Ethernet sets out the format of data packets. This layer handles transmission errors and passes data to the physical layer.

What is a virus?

A virus can replicate itself and spread from system to system by attaching itself to infected files.

A virus is only activated when opened by a human.

Once activated, a virus can change data or corrupt a system so that it stops working.