Studied by 3 people
Abstraction
process of removing unnecessary information from a set of instructions so that it is simpler, more relevant and can speed up the program
Bus
Set of wires connecting components within the CPU
Advantages of networks
Sharing resources can save money
data is easy to back up
Easy collaborative working
Advantages of bus topology
cheap and easy to install
Advantages of star topology
reliable, if one device fails the whole network isn’t affected
High performing as no data collisions occur
More secure- not all devices receive data sent (unlike in bus topology)
Application software
Computer software that allows the user to carry out a specific task, eg browsers/ games
Arithmetic logic unit
In charge of all maths and logic problems within the processor
ASCII
7 bit character set
Binary search
Takes the middle of an ordered list and removes the lower/ higher half depending on wether the input is lower or higher than the middle value, continues this cycle until only the searched for item is found
Breakpoints
Can be added to code by a programmer, which will pause the programs execution so the programmer can observe results.
Bus topology
Devices connected via one cable
As more devices are added, performance decreases
When data is sent, all devices receive it (only the intended recipient processes it)
If main cable falls, the whole network will crash
Cache
Memory that is very fast and is easily accessed by the CPU, it allows requests to be served quicker since its quick to read/write
Computer system
A combination of hardware and software
Computer virus
self replicating
Damage or delete files on a computer
Can be spread computer to computer
Control unit
Directs and coordinates most of the operations inside the cpu
CPU
Processes and uses data to perform tasks
Register
Memory locator inside CPU, store information that ALU needs to carry out current instruction
Decomposition
Breaking down a problem into smaller, sub problems, each with an identifiable task
Definite iteration
Repeating a block of code for a finite number of times
Disadvantages of networks
expensive / may need to hire a network manager
Hackers / viruses can infiltrate the network more easily
Embedded system
A device developed for a single purpose (which has a system embedded into it in order to fulfil that purpose) , eg washing machine, microwave
Fetch decode execute cycle
fetch- instructions are fetched from memory, it is them carried to the control unit
Decode - control unit decodes instructions, if arithmetic or logic is needed, instructions sent to ALU
The instructions are then executed (may require additional data held in memory)
Field
A single data item within a table
Foreign key
A field in one table, that is a primary key in another table
Primary key
A unique identifier that will have a different value for each record in a table
Function
A name of a section of code that performs tasks and returns a value
General purpose system
A computer system that can change its purpose by adding more software
Global variables
Variables declared in the main body of the program and can be accessed anywhere in the code
Graphics card
Used to process the graphics portion of the processing load
Hard drive
Stores majority of data and houses the hard disk
Hardware
Physical elements of a computer system
Lossless compression
A form of compression where none of the original data is lost, for example Huffman coding
Lossy compression
A compression technique that works by discarding some of the data to reduce the amount stored. (Can result in the deterioration of quality)
Huffman coding
Reduced the number of bits by encoding more frequent characters with shorter bit representations and less frequent ones with longer bit representations
Indefinite iteration
Repeating a block of code until conditions are met, eg while loop
Linear search
Works by starting at the beginning of a list and moving through values until it either finds what it is searching for, or reaches the end of the list
Local variables
A variable declared within a function, and therefore can only be accessed within that function
Logic error
An error in the logic of the code that causes it t run incorrectly, but not to crash. (So the program works, but not as the programmer intended it to)
Magnetic media
use read write heads
Contain electromagnets on the surface
Split into sectors of magnetised regions
Require movements (therefore not as robust as SSDs
Have a spiral track
Optical media
disks eg cds and dvds
Light is shined onto them
Have a spiral track and rotate
Consists of a series of pits and lands each of which reflect differently when the light is shone onto it, and can either represent a 1 or 0
Parameters
A variable that can be passed through a subroutine
Phishing
Usually an email that falsely claims to be from a legitimate enterprise, in order to trick the user into sending private information
Blagging
The fabrication of an elaborate story in order to trick a user into sending money/ giving away personal information
Network Protocol
Rules for communication between two or more computers
Records
Complete sets of information that consist of fields.
Run length encoding
Works by reducing the physical size of a repeating string of characters by representing the number of times the character repeats, followed by the character. Eg AAHHH would be 2A3H
Sample resolution
The number of bits used to represent each sample
Secondary storage
Non volatile memory that is used to store data permanently, not directly accessible by the CPU
Solid state drive
A form of flash memory that is retained even when there is no power- more robust than magnetic and optical due to no moving parts.
Spyware
A computer program which is installed without permission, sometimes through a virus, it collects data and sends it back to another source
SQL
Structured query language, a program language that is designed to manage data within a database.
Syntax error
An error that occurs when the rules of the programming language is broken, results in the program crashing.
Trojan
A piece of software that is ‘disguised’ as another application (eg utility/ game) and performs malicious activities like releasing viruses or installing spyware whilst the user is unaware.
Clock
A part of the cpu that synchronises all instructions, each instruction is carries out on an electrical impulse that is controlled by the clock
Types of social engineering
blagging
Phishing
Shouldering
Shouldering
Observing someone enter passwords/ personal information. Eg watching someone enter their bank pin in order to steal money later.
Compilers
translates whole code into machine code before it is run
Can store compiled code as an executable file
Interpreted code
translate code into machine code line by line (so makes errors easier to spot)
Does NOT save machine code
Advantages of compiled code
makes it easier to distribute code, since the executable file can be shared rather than the source code (less risk of companies stealing machine code)
faster since they’re not line by line
code only has to be translated one instead of each time it is needed to be used
No installation needed.
Advantages of interpreted code
convenient when developing a program (debugging is often easier)
TCP/IP stack
application
transport
Internet
Link
Application layer
http, https, smtp, IMAP and Ftp operate at this layer
This is where network applications eg browsers/ email programs operate
Transport layer
sets up communication between two hosts (computers)
Agrees settings eg size of packets
TCP and UDP operate at this layer
Internet Layer
where addresses are added to packets
IP operates at this layer
Link layer
where network hardware is located
WIFI and Ethernet operate at this layer
HTTPS
allows computers to send/ receive web pages
IP
Adds addresses to packets of data so that they arrive at the correct destination when sent over the internet
SMTP
Protocol to send email
IMAP
Used when receiving emails
FTP
Protocol used when files are transferred from one computer to another over a network
Used by web devs when uploading web pages to web server
Ethernet
Family of related protocols rather than a single protocol
Used by LANs
Wi-Fi
similar to Ethernet - family of related protocols
WLAN (used by comps in a wireless network)
PAN
personal area network
Group of computers connected around an individual (usually using Bluetooth)
WAN
wide area network
Group of computers connected over a large geographical area/ global scale
Collective or distributive ownership
LAN
Local area network
Connected over one building/ site
Uses Star/ bus topology
Benefits of standalone computer
less malware risks/ hacking
Faster speed (since networks can become slow as usage increases)
No need to employ network manager (so cheaper)
Benefits of networks
hardware devices can be charged (eg printers) - so cheaper
Data/ files can be shared easily, so collaborative working is easier
Central management can handle backups
Work can be accessed from any computer on the network
Computer usage can be monitored by employers
Advantages of wireless networks
usage anywhere in range
Not limited by cables
No cable cost
No trip hazards
Very easy to add new computers to network
Diss advantage of wireless networks
slower network speed than wired
Not as secure
Signals can be affected by other electrical devices
How is CPU performance affected
by clock speed - higher clock speed = more executes per second
Increase num of cores = more executes at same time
Increase cache memory - more data/ instructions can be fetched from fast memory
Embedded system
computer system inside another device usually designed for a specific purpose
Converting a sound to digital format
Analogue sound is converted to an electronic signal
Strength of signal is measured at regular intervals (samples)
Each sample is rounded to nearest lvl and represented as a bit pattern
Misconfigured access rights
access rights that have been set up incorrectly, giving the wrong people access to things they shouldn’t have access to
Pharming
A cyber attack where traffic for a website is redirected to a fake website
Removable media
devices used to store data that can be moved from one machine to another
Not very safe - could get lost/ carry sensitive data
White box penetration testing
done by someone who has some access rights/ knowledge of system, but not all
Used to simulate an internal attack (eg rouge employee)
Black box penetration testing
done by a person who has no knowledge of system/ no access rights
Used to cumulate external attack
Biometric measures
Examples include fingerprint scans, face recognition, retina cans
Used to biologically identify an individual
Automatic software updates
improve security - allow programs to be patched
Does not rely on person remembering to update
Captcha
Completely automated public Turing test to tell computers and humans apart
Inserting using SQL
INSERT INTO (specifies tables)
VALUES (states new data value)
Deleting data with SQL
DELETE FROM (specify tables)
WHERE (conditions)
Using SQL to edit data
UPDATE (specifies tables)
SET (specify fields)
WHERE (conditions)
Cloud storage
Uses magnetic/ SS in a remote location
Can be accessed from any computer with internet connection
Storing data on optical media
Surface has pits and lands that reflect light differently each represents a 0 or 1. Light sensors detect this and it is converted to binary and processed by cpu
Storing data on a hard disk
Surface of each disk is divided into concentric circles called tracks. Intersection of track and sector is called a block. Block =magnetised region. The magnetism represents a 0 or 1, this is detected by a read write head, converted to binary and processed by cpu.
Comparison of all storage types
SS is faster than magnetic, is also smaller, lighter and generates less heat, more robust
Magnetic is cheaper per byte and has large capacity
Optical is very cheap but low capacity and slow access time
Note 
Flashcard (106)