Terms in this set (108)
Fetch Execute Cycle
Load address to program counter.
Load program counter to Memory Address Register.
Update PC to next address.
Calculate data in the ALU.
Processor goes back to PC to find next address.
Three types of Systems
Dedicated - Computer system dedicated to one task eg. Robotic arm.
Embedded system - Dedicated system within a larger system eg. Dashboard.
General purpose system - Used for many different purposes eg. Personal computer.
Basic Input/Output System
Stored in the ROM, Loads operating system during boot.
MAR: the memory address of the next piece of data that needs to be fetched.
MDR: temporarily stores data from the memory.
Program counter: continuously provides the CPU with the address of the next instruction.
Accumulator: stores data from ALU
Bus: physical pathway which transports data between components. Created in 1940's
Data size measurements
Byte = 8B its
KB = 1024 Bytes
MB = 1024 KB
GB = 1024 MB
TB = 1024 GB
Backs up all the data on the system,
Only backs up new/ updated files.
Server: Types - Database, Web, File, Mail
A computer that holds data to be shared with other computers.
Database - Allows client computer to access a central database.
Web server - Uses HTTP to server requested web pages to client machines.
File server - Central place to store files that can be accessed from anywhere.
Mail - Sends, receives and stores emails eg. Gmail.
Ways of testing a system.
Uni testing - Checks that each component of a system is working.
Validation testing - Checks the type of data that the system can use.
Volume test - Testing the amount of data a system can handle.
How does a program 'Fall gracefully'
The program will take steps to make sure that there is limited data loss when there is a fault. This could be by making a dump file.
Factors that can negatively effect a system.
Software could contain errors,
Ways to lower the potential damage of a System Disaster.
Creating Backups and storing them in a safe location.
Having secondary power sources,
Making a 'Disaster plan',
Redundancy, having reserve recourses available incase of a crash.
When a computer system has no free memory left in RAM, data will be swapped to a dedicated area on the hard drive from the RAM. When the user needs the data again it will swap it back. It's slower then normal RAM. Controlled by OS.
Flash memory is programmable and erasable. It is non-volatile so it is ideal for portable storage.
It's being used as ROM as it's programable.
It's is expensive.
A set of instructions that resides on a storage device, like a hard drive, and can be loaded into computer memory and executed.
SSD Storage: Uses, Adv's, Disadv's
Allows for portable technology like smartphones.
USB drives, laptop hard drives, Camera memory.
Small, no moving parts, fast read and write.
Expensive, can wear over time, durable.
Optical storage: Uses, Adv's, Disadv's
A track of pit spirals that can be read with a laser to represent ones and zeroes.
Storing media on DVD's.
Cheap, portable, widely available.
Limited capacity, easily damaged, slow data rate.
Magnetic storage: Uses, Adv's, Disadv's
Contains a drive arm with a read/ write head which reads and writes data from a rotating magnetic disk.
Desktop PC's, Network storage, Backup systems.
High capacity at a low cost, fast data access.
Will eventually fail, large, moving parts.
Types of Malware
Virus: A program hidden within another program or file.
Worm: A malicious program that acts independently and can replicate and spread.
Trojan: A malicious program disguised as a legitimate piece of software.
Spyware: Secretly passes information to a criminal.
Adware: Displays targeted advertising and redirects search requests.
Ransomware: Limits or denies a user access to their system until a random is payed.
Pharming: The redirecting of a users website to a fraudulent site through their DNS.
Backdoors - A way of gaining access to a program or computer. Often they are created using a trojan horse.
Three types of social engineering
Phishing: Impersonating someone to try and a get personal information from a user.
Shouldering: A technique of trying to record somebody who is inputting personal data.
Blagging: Carried out face to face. Try to persuade people to give up personal data.
Methods of attack:
Brute force attack,
Repeated tries to get into a system using different usernames and passwords. Prevented by complex passwords.
Denial of Service attack - trying to flood a website with data traffic. DDoS is an attack from multiple sources.
A method of intercepting data containing sensitive information before it reaches it's location using a packet sniffer. Prevented by encryption.
Uses the same 'Structured Query Language used to manage large data bases by using commands as usernames and passwords. Prevented by careful validation
When sensitive data is stolen from a company - could make the company liable under the Data Protection Act. Often data is taken by workers through USB's or laptops left in public.
Firewalls: Controls the transmission of data between a computer and a network. It can be configured to apply rules to certain connections. It can be Hardware or Software.
Anti-Malware: It's designed to spot a malicious program and to remove it from a system/ network. Must be regularly updated.
Encryption: Converts information using a Public Encryption Key into a form that can't be read if it's intercepted.
Network forensics - Monitors and records data that passes through a network. Attacks can then be analysed so they can be prevented. Can be used to monitor inappropriate activity from inside the network.
Penetration testing - Trying to find vulnerabilities within a system so they can be reported.
Computer security - People
Policies - Rules written by organisations that concerns the usage of their network. Could relate to bringing data home from work or password security.
User access levels - Limits the data that a user has access to read and write based on permissions and their position within an organisation.
Blocking USB ports - Prevents data being taken from the business on removable media which is against the data protection act.
Blocking dangerous websites - Decreases the chance of users accidentally downloading malware.
Blocking physical access - Keycards and locks and physical security procedures should prevent staff from allowing people into the physical network area.
User access levels: limit the information a user can access or edit.
Passwords: Prevent peoples accounts from being accessed without permission.
Operating System: Key functions - Memory, Files, Users, Peripheral, GUI's, Interrupt, Networking
OS is the link between Hardware, Software and the User:
- Memory management: Makes sure programs can't delete data stored in ram + virtual memory.
- File management: Orders files into directories and folders.
- User management: Accounts with passwords and different access levels.
-Peripheral management: Device drivers communicate with hardware eg. Mouse, headphones.
- GUI's: Drag and drop.
- Interrupt handling: When a new program or process needs to star an interrupt signal is generated by the OS and handled - blocks process eg. Mouse is clicked.
- Networking: Protocols
It .needs to be updated regularly for security setting and drivers.
Utility software - Uses
Utility software performs specialised tasks support the OS:
-Backup software: Backs up files to external storage or the cloud (Full/ incremental).
-Encryption software: Encrypts data on hard drive or removable media. Requires password to decrypt, useful for following Data Protection Act.
-Compression software: Shrinks file sizes. Run length encoding looks at repeated data and shrinks files. Must be lossless.
-Defragmentation: Moves fragments of files closer together so read time is faster. SSD's don't often need it as it can reduce it's lifespan.
Network: Types - LAN, WAN, VPN, Wired, Wireless
Networks are linked computer devices which are linked so they can communicate and exchange information.
LAN - consist of devices located in a single local area by one organisation.
WAN - connect multiples LAN's together, possibly over a long distance.
VPN - A LAN which is connected to via a public network eg. Internet. Deals with encryption.
Wired - Network where devices are physically connected by cables. Faster then wireless.
Wireless - Uses wireless communication through microwaves, slower, less hardware.
Network performance: Measurements, Causes
Bandwidth - Maximum rate of data transfer.
Throughput - Actual rate of data transfer.
Latency - Delay between a packet being sent and received.
Jitter - Change in delay of packets.
Packet loss - percentage of packets lost or corrupted during transmission to receiver.
Network congestion - Where too many people are using the same switch or hub.
Malware attacks eg. Viruses.
Examples of Network Hardware
Network Interface Controllers: These plug into the motherboard of a computer. They allow it to access a network using transmission media eg. Wifi, ethernet.
Network Switches: Advanced hub that makes use of all ports and bandwidth to transmit packets without collisions.
Routers: They connect networks together.
Transmission media: A term used to describe ways network devices are connected eg. Ethernet cables, Fibre optic cables which transmit data as flashes of lights, Wifi - Radio waves.
Hubs - Used to connect many computers together. Broadcast the input signal from port to all other ports. Used to make a star network.
Bridges - Connect two networks or network signals together eg. Two LAN segment.s
Cloud computing: Pros & Cons
Term used for services and infrastructure accessed via the internet. Software can be offered as a service - SAAS. Allows for easy backups and software updates, can be accessed anywhere, must have internet connection.
IAAS or Infrastructure as a service allows companies to rent infrastructure for processing or storage of their data.
Pros: Can access data from anywhere. Often cheaper due to need for specialist staff. Easy to back up data. Often allows extra storage.
Cons: Requires an internet connection. Heavy reliance on third-party. More vulnerable to hacking and other threats.
At the centre of the network is the server. Each device transmits data through the server.
-If one device fails it will not effect the others.
-Problems can be identified quickly
-Less cabling then mesh
-If the server fails the network collapses.
-Requires hardware and physical cabling.
Every device with in a network is connected to every other device using wifi or bluetooth.
-All devices help share network load.
-A device failing will not effect the network.
-Network is difficult and expensive to setup and maintain.
Bus and Ring topologies
Bus networks have a central spine connecting all the devices.
Ring Network has the devices set up in a circle.
Any device connected to a network.
Rules that devices in a network must follow to effectively communicate.
Ethernet: Used to connect NIC's, Routers, and Switches. It can handle large amounts of data.
TCP/IP: Allows computers on multiple networks, including the internet, to transmit and receive data packets.
HTTP: Used by Web servers, clients and browsers.
HTTPS: Used for secure communication between service and client.
FTP - File transfer protocol used to send files through a network (SFTP) - secure.
IMAP - Internet message access protocol, allows access to an email server.
Layers refer to a set of protocols with specific function. Data can be transmitted between adjacent layers. They contain both software and hardware
Application layer: Data relevant to Browsers and Email clients eg. HTTP.
Transport layer: Ensures that data is sent and received directly between network hosts, returns if errors - TCP.
Internet layer: Communicates the IP addresses of all devices used in data traffic, assembles packets.
Data link layer: Concerned with physical data transfer over layers. Pros: Layers can be taken out and edited without affecting other layers. Allow different developers to concentrate on different aspects of a network
Allows users to access a specific computer - the host - via a network connection.
Web-Hosting companies use this on a large scale, renting spaces of their networks for people to run websites. Servers are located in racks and can be uploaded to using FTP.
Packets are small units of data split up to be sent through a network. Each packet has:
- Source and destination IP
- Packet sequence reference
- Checksum to check for errors at the destination.
Each packet makes their own way to the destination where they are reassembled. Routers decide where to send the packet based on distance and network traffic.
Store personal information about your browsing habits.
Accessible data files saved on your computer containing internet history.
The social and economic gap between those who have access to the internet and those who don't.
This lack of access can expand the divide further because some jobs are only advertised online.
Key laws: Data protection act
Computer Misuse act
Copyright, designs and Patents act
Freedom of information
Created to protect the personal information held about individuals within organisations. You have the right to see data stored about you.
Designed to prevent hacking and damage to computer systems eg. DDoS.
Deals with copyrighting works such as documents or music. Anything you design is copyrighted to you.
Allows creators to share their work with conditions of use eg. Attribution, Not for commercial use.
Provides the public with rights to information stored by governments.
Algorithmic features: Repetitions, Selection, Data structures, Parameters, Functional decomposition
Repetition - Iteration is repeating code. Recursion is in a function
Selection - Running different parts of an algorithm based on a decision.
Data structures - Array's, lists', records ect.
Parameters - Limits on inputs eg. Two digits.
Binary search: Looks for a specific value in an ordered lister by checking percentile 50 - 75/25 ect.
Data must be ordered but can search through many values quickly.
Linear search: Iterates through a list comparing each value with the value being searched for. Not very efficient but works with unordered lists.
Sorting algorithms Pro's & Con's: Bubble, Merge, intersection
Bubble sort: The first pair in a list are compared and sorted. Then the next pair ect.
Pros - Large numbers can pass very quickly from left to right.
Cons - Small numbers can't - inefficient.
Merge sort: Data is repeatedly split into halves until each list contains only one item. The items are then merged in order.
Pros - Good for parallel. processing (multiple cores). Very efficient.
Insertion sort: Each item in an unordered list is examined in turn and compared with the previous item on the list. Higher values are left in the same position.
Pros - Good for small data sets.
Cons - Inefficient.
Flow Chart Symbols: Terminator, Input/output, Decision
Terminator - Oblong with curved corners.
Input/output - Parallelogram.
Decision - Diamond.
Subroutine - Oblong with two vertical lines at either side.
Process - Oblong.
Data types: Integer
A whole number
1/0, yes/no, on/off
A single letter or symbol
A collection of alphanumeric data
Devices that connect to computers to add function or use eg. mouse.
Two types of Ram
DRAM - Dynamic RAM. Uses a capacitor to store data. As they loose their charge DRAM must be constantly read and written back.
SRAM - Static RAM uses transistors that don't need to be constantly refreshed. Often used as cache as it is more expensive.
Features of a GUI
Drag and Drop,
File/ data management and visualisation.
A network where a main computer server is accessed to have a service requested from multiple client computers.
Pros - Allows for easy backups and software updates, expert admins can look after server, secure.
Cons - Difficult to setup and maintain, requires hardware. If the server fails, network collapses.
All computers within the network act as both a client and server. They all share files programs and access levels.
Pros - If one device fails network stays up. Easy and cheap - no extra hardware. Each device can access every other device.
Cons - Not very secure, difficult to backup.
Media Access Control address which is given to every NIC (card that plugs into motherboard and communicates with transmission media)
IP Address: Static & Dynamic
An address which is assigned to network devices to allow data transfer across the internet.
Static addresses are permanently assigned to a computer or server by an ISP
Dynamic addresses are assigned by a router within a network every time the network is restarted.
Usage of technologies like CGI and VR to make an immersive experience.
Driverless cars: Pro's & Con's
Could solve the problem of traffic.
Lower the rate of accidents
Could be very expensive.
People could loose their jobs
Creative work that's not copyrighted and therefore free for you to use whenever you want.
Trying to cause no harm to others and acting in a morally responsible way.
The impacts of technology on the environment: Pro's & Con's
Reduces use of paper.
Mobile and home working reduces transportation costs.
Smart devices control their power usage.
Increased energy consumption.
It is difficult to recycle waste.
Cost of transporting raw and synthetic materials for producing devices.
Open source & Proprietary: Pro's/ Con's, Examples
Open source software is intended to be shared openly online with no restrictions.
Pros - Allows people to learn from it and use it as inspiration for their own projects. Derivatives can be made so the program can be improved collectively. Can reach a larger audience.
Cons - No control over how people use it, can't make profit.
Eg. Linux, Python
Proprietary software is owned by and a license to use it can be purchased.
Pros - Can control distribution and make money. No one can take advantage of your work.
Cons - Can't be used to help anyone else with their products. No derivatives.
Eg. Photoshop, Skype.
AND = ^, Semi circle
OR = Reverse , Curved semi circle
NOT = ⌐, Circle
Pseudocode: Casting, Inputs, Outputs(concatenation, escape characters), IF's
Casting: Turning one data type into another eg.
Inputs: Receiving information from the user: input("Age")
Outputs: Concatenation is joining strings eg:
print(str1 + str2).
Escape characters are used to format eg. print("ab /n cd")x
If 5> 8 then
File operations: Reading one line & all lines
Reading a line:
myFile = openRead("file.txt")
x = myFile.readLine()
Reading all lines:
myFile = openRead("file.txt")
while NOT myfile.endOfFile()
Databases: Fields, Records, Primary Key, Flat-file, Relational.
Fields are categories.
Records are each row of related data.
Primary Key a unique identifiable field that cannot be repeated.
Flatfile is a database that has only one table.
Relational databases have more then one table.
Arrays: Dimensions, Creating, Looping
A data structure for storing groups within a program.
One-dimensional arrays have a single list of common elements.
Two-dimensional arrays can have an array in each of it's elements.
Creating an array:
array users [rows, columns]
Looping through an array:
for i = 0 to 9
Sub-programs: Arguments, Parameters, Procedures, Functions
Contain a function used to save time and avoid repetitive code.
Arguments refer to actual data within a Sub-program.
Parameters refer to variables within a Sub-Program.
Procedures are a set of functions grouped together under a name.
Functions are designed to return a value.
Defensive design: Authentication, Validation/ verification
Defensive design is how a program is designed in a way that considers those that will use it and their access levels.
Authentication - Checking information is correct eg. Comparing it to a value in a database. Three types of authentication: Something you know eg. Password. Something you have eg. Keycard. Something you are eg. Fingerprint.
Contingencies like backups and password recoveries are necessary.
Validation/ verification: Checking that data is plausible and possible eg.
Data type checks,
Format checks eg. Postcode,
Program maintainability: Strategies
A well maintained program is easy to understand and straightforward to access and edit.
Comments - Personal notes to explain the code
Indentation - Separates statements visually
Variables - Should be sensibly named. Snake and camel case.
Sub-routines - Used to combat repetitive code
Testing is essential before a program is released to the public.
Iterative - A cycle of design, development and testing.
Final - Carried out by real users to find issues.
Performance - What impact does the code have on your system resources.
Usability - Ease of use
Security - Testing vulnerabilities.
Load/ stress - How much traffic can it handle.
Errors: Syntax, Logic
Syntax errors are usually typos.
Logic errors are faults in structure or design.
Data: Normal, Extreme, Erroneous
Test plans & Possible headings
Values at the limit of what a program can process,
Data that should not be accepted.
Test plans are tables like iPod tables that can be filled out to test the reliability a program.
Headings of a table could include: Test number, Test data, Test description, Expected outcome, Actual outcome.
Programming languages: High/ Low level, Machine code
High level contain keywords and syntax so they are easy for us to interpret.
Low level are normally more difficult to read and write.
Machine code is a low level language that can be read and executed without translation.
Translators are used to translate a code so a computer can execute it.
Assemblers - Used to convert low level languages.
Compilers - Used to convert high level programs, as a whole. If there is an error it must restart
Interpreters - Used to examine high level languages line by line.
Integrated Development Environment (IDE) : Code editors, Error diagnostics, Run-time environment, Translators
IDE software helps programmers to design and develop their program.
Code editors - Text editor designed for writing code.
Error diagnostics - Help identify errors.
Run-time environment - Allows programs to be run virtually line by line to look for errors.
Translators - Translate code into machine code.
Temporary memory used by the processor to store data needed for executing tasks.
A software managed network within an existing physical network.
Compression: Pros & Cons
Taking original data and compressing it so it takes up less data. Done to save storage space or when sending data across a network with limited bandwidth.
Lossy - Compression where some information is lost. Usually not noticeable to the user eg. JPEG.
Pros - Even though the decompressed file isn't identical to the original the difference isn't noticeable. Greatly decreases file size so can be sent by email.
Cons - Data can be lost
Lossless - Looses no data eg. PNG, GIF.
Pros - No data is lost.
Cons - Does not compress as much.
Internet of things
Connection of everyday objects to the internet eg. Fridges.
Centreal processing unit.
It is the brain of the computer made out of an 'Input, process, output system'. It's responsible for the processing carried out by the computer.
It has a 'clock speed' in Ghz - Billions or calculation per second.
Features of the CPU: CU, ALU, Address bus, Data bus
Control unit coordinates timings and the flow of data in the CPU.
Arithmetic logic unit is responsible for arithmetic calculations and logical comparisons eg. 5==5?
Address bus requests data from an address in memory.
Data bus moves data in both directions from memory as it is read and written.
Registers small storage areas within the CPU where binary digits are stored.
Registers in the CPU: Accumulator, PC, IR, MAR, MDR
Accumulator - Stores results from calculations of the ALU until they are written into memory.
PC - Program counter stores the memory address of the next instruction to be executed. Incremented by 1 after each cycle.
IR - Instruction register stores the current instruction in binary.
MAR - Memory address register stores the current address of the instruction being executed.
MDR - Stores data that was read or written to memory.
Primary storage - similar to RAM. Its faster and more expensive. It stores data frequently accessed by the CPU.
Level 1 cache is placed next to the CU and ALU to store instructions - small amount of data.
Level 2 and 3 cache will be checked if the required data is not in the level 1, they are slower to access. Multi core processors normally have a shared level 3 cache.
Multi core processors.
Dual core processors have two cores and can process data in parallel. Usually they have a shared layer of level 3 cache. They are able to process data twice as fast as single cores.
RAM & ROM
RAM - called random access memory as an memory location can be accessed in any order. When you run a program it gets copied to RAM, then ran by the CPU.
ROM - Read only memory used to store BIOS. Some devices like a digital camera will have ROM built in so it contains programs needed to run the device.
Flash ROM allows the ROM chip to be edited, this allows software updates.
Secondary storage characteristics
Capacity, Speed (read and write data rate), Portability, Durability, Reliability.
The internet is made of interconnected networks. Uses the TCP/IP protocols to allow computers to communicate. Generally uses client, server models.
Modem - Take digital data and encodes it into analogue data. eg. Sound wave into binary. Broadband is used for modems that are always connected and share connection with the telephone.
Routers - Connect to transmission media. Receive packets of data and redirect them to the next router of final destination.
Domain name service - Domain name deals with mapping domain names to IP addresses.
If a browser is visiting a domain it will first check to see if the browser has the address cached then it will request it from the DNS.
Ethernet & Wifi
Ethernet is the standard used for connecting computer together with with cables.
Contains a standard number which is specific to the type of cable it is.
Wifi is the standard for wireless communication between computers.
Works at microwave frequencies of 2.4 and 5gHz. Each wireless access point uses a specific channel of 22mHz of bandwidth. If two wifi networks are operating at the same frequency there's a a risk of interference.
Encryption encodes information so it can't be read without a key to decrypt it. Wifi networks must be encrypted as they can be intercepted. Old standards: WEP, WPA. WPA 2 is used now. Most wifi uses a PSK - pre stored key on all devices to decrypt data.
Operating system: Structure
Centre of an OS is the kernel which deals with low level operations like memory management. Multi-tasking OS's can run different processes at the same time by allocating a small amount of the CPU to each process.
Around the kernel is the shell that contains the GUI.
Ethical, Cultural and Environmental issues
Ethical - Right to privacy eg. Cookies allow websites to track where you visit on the internet. Photos of houses are stored in mapping services.
Informed consent is required but not often received.
Cultural - Many low skill jobs like manual labour are being automated. Offshore outsourcing is getting people across the world to work for your company eg. Call centres. Digital divide - Economic divide between areas the do and don't have access to the internet eg. Education, cheaper bills, job opportunities.
Environmental - Computers use large quantities of raw energy and recourses. 2% of all energy used to maintain and air condition data centres. Electronic waste often dumped on developing countries, toxic elements can harm the population.
Breaking down a complex problem into smaller, more manageable parts eg. Racing game into: AI, Gameplay, Graphics.
Smaller parts would often be developed as a sub-routine.
Abstraction & Generalisation: Control & Data
Removing unnecessary data and detail to make a problem easier to solve eg. London Underground Map.
Generalisation is trying to find a solution to a problem that can solve many different problems eg. Program draws a square by moving and turning 90' four times Or A program takes an input of degrees, turns and distance, to draw a polygon.
Control abstraction is using subroutines.
Data abstraction is using data types instead of binary.
Algorithms: Creating them
Algorithms are step by step instructions to solve a problem. Can be used by a computer to automate a problem.
Steps to creating one: State the problem precisely, Break it down - decomposition, Find patterns - abstraction, create step by step solution.
Subroutines, Functions, Iteration
Sub routines are used to avoid repetitive code.
Functions are subroutines which take an input and return an output.
Iteration is repeating sections of code. Iterator is the value which changes each time.
Variables: Assignment, Initialisation, Cases
Variables are identifiers which point to a memory location storing a value. Constants don't change when a program is run.
Assignment is giving a variable a value.
Initialisation is when a variable is first set up.
Cases: Snake case is using an order-score instead of a space. Camel case is starting words with a capital letter
Numeric operations: Operand, operation, operator
Mathematical operations have an operand: input,
operator: + - /.
Examples of operators: Modulus finds the remainder
eg. 13%5 = 3
Integer division uses integer values before decimal point eg. 365 DIV 30 = 12.
Exponential is to the power eg. 2^4 = 16.
If and Boolean statements
Booleans are true or false values. They are combined with boolean operators.
true AND true = true
False OR true = true
NOT false = true
5 > 3 = true
3 >= 3 = true
5 == 3 = false
4 != 2 = true
Nested if's and Switch Case
If statements placed inside an other. Often cause complicated and cluttered code. Can be simplified with Switch case.
Switch case - Used to give different outputs depending on the input without excessive code eg.
x = input("Enter value")
Loops: While, Until, For
Loops are used to avoid repetitive code. Repeating a section of code is called iteration.
While - Run through a loop on a condition eg.
Until - Checks condition at the end of the loop eg.
run this code
For - Used to repeat a loop a certain number of times eg.
for i = 10 to 1
String manipulation: Characters, Cases, Length, Substring, Concatenation, ASCII codes
Finding particular characters:
string = "hi"
print(string) = "h"
print(string.upper) = "HI"
print(string.length) = 2
string1 = "eight"
print(string1.substring(1,4) = "Ight"
print(string1 + string) = "eighthi"
print(asc("a")) = 65
print(chr(65)) = "a"
File opening: Closing, Opening models
Files must be closed because when a file is opened the OS allocates it a 'file handle' of which it has limited numbers. The OS may also lock it while it's opened.
File opening models: Read, Write, Append - adding to end of file.
Binary: Shifts, Overflow errors, Underflow
Binary stores data in ones and zeroes.
Shifts are moving all binary digits left or right. Right is dividing data by 2, left is multiplying by two.
Overflow errors happen if a calculation goes over a bit limit.
Underflow is shifting numbers out of the right. Can lead to a result of 0.5 less eg.
011 = 3 . RIGHT SHIFT
001 = 1
Show what base you're using eg.
0010 2 OR
Hexadecimal: Denary to hex
Base 16 numbers 0-15/0-F.
Denary to hex:
Divide by hex base and find remainder eg.
243/16 = 15r3 , F3
A way of converting binary into characters.
ASCII is the American standard code for information exchange. Can store up to 255 characters.
Unicode international system that can store many characters for languages like Chinese.
Images: Bitmap, greyscale, Colour
Bitmap - Made out of ones and zeroes representing black and white
Greyscale - Storing different shades of grey in images. The more bits per pixel, the more colour combinations.
Colour - Full colour images store 8 bits of R&G&B for each pixel allowing 2^24 combinations.
Sound cards contain an ADC - Analogue to digital converted which takes samples of sound at fixed intervals. Hz is the number of samples per second. DAC used in speakers.
How defragmentation happens
When files are deleted spaces are left in the har-disc between data. If a new file is saved into the space it may not fit meaning it will be fragmented. If a file is edited the new data may need to be stored at a different part of the hard disk
Issues with demand for latest technology: Ethical, Environmental, Technological
Ethical - Contributes to digital and social divide. Pressure on parents to upgrade children phone. Stigma attached to owning old devices. Phone's are fragile so people will upgrade.
Environmental - E-waste dumps develop in poorer countries. Many working devices are disposed of. Releases toxic waste into the land. Waste of resources, leads to over extraction of raw materials.
Technological - Leads to technological advances. Phones hardware is not often upgradable or replaceable. Poorly designed durability of some devices.
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