COMPSCI 111

Computer Science

What key design principle is used for computer hardware?

Modularity

What do system units come in?

Form factors

What are the different types of form factors?

• All-in-one pc

• Tower

• Desktop

• SFF

• USFF

What is the PSU?

Power Supply Unit, converts AC to DC voltage

What is the motherboard?

Main circuit board to which all components are connected, allowing them to communicate with one another

What is the CPU and how does it work?

• ‘Brain’ of the computer - processes data in computer using its instruction set

• Performance measured instructions per second

• Clock speed (Hz) measures speed of electrical signals passing through processor,

• Must be kept cool, mostly with fan

What is the law for the number of transistors and what does it state?

Moore’s Law - ‘The number of transistors on a single integrated circuit doubles approximately every 18 months, while the price remains the same‘

CPU - other measures

• Power efficiency and heat as important as clock speed

• Modern CPUs have more cores = increasing processing capacity

  • New type of processors - SoC (system on chip) used in mobile + embedded devices

Features of primary memory?

• Used to store data for quick access by CPU

• Main form is Random Access Memory (RAM)

• RAM is volatile memory

• More RAM = better computer speed by providing more quick access memory

• Capacity measured in bytes, clock speed in Hz

• Many types of RAM, most common type is DDR3 SDRAM

• CPU cache faster than primary memory

Features of secondary memory?

• Long term file storage - repeated access

• Non-volatile

• Many forms:

  • SDD

  • HDD

  • CDs, Blu-Ray, DVDs

  • USB drives external HDDs

HDD

• stores data on spinning magnetic disks, data is written and read by moving heads

• cheap, widely used/supported, large capacity, long operating life

• noisy, consumes more power, fragile

SSD

• stores data on flash memory

• silent, higher read/write, low power usage, more durable, takes up less physical space

• costlier, wears out faster

Redundant Array of Independent Disks (RAID)

• pools SSD/HDD tgt to form larger, more reliable data storage mechanism

• each config has own strengths + drawbacks

• commonly used in servers

• two configs - RAID 0 and RAID 1

  • RAID 0 - horizontal data stripes to increase speed

  • RAID 1 - vertical data stripes increased reliability

  • RAID 10 - uses RAID 0 in RAID 1

Memory Heirachy

Access time decreases while cost lowers and capacity increases from CPU cache to secondary memory.

Expansion cards

• additional circuit board that provides extra functionality

• eg. sound card, network card graphics card

Graphics card

• Graphics processing and runs computer’s monitors

• contains:

  • GPU

  • Own video memory

  • Heatsink and fan

  • Ports

Connectors and buses

• peripherals are connected to motherboard via ports

• ports form part of a bus

• wired and wireless connections

Email

• Electronic Mail - system for sending and receiving messages over the internet

• Asynchronous

• Recipient address required to send email message

Email composition

• Header

  • Sender

  • Recipient

  • CC

  • BCC

  • Subject

• Body

  • Message

Email protocols

• protocols are standards for communication

• email protocols are used by email clients

• SMTP (Simple Mail Transfer Protocol)

  • sending emails from client to server

• POP3 (Post Office Protocol v3)

  • emails downloaded from server to client then deleted from server

  • internet not required to read downloaded messages

  • is downloaded locally so difficult to access from different clients

• IMAP (Internet Message Access Protocol)

  • Downloads copy of email from server to client and retains email on server

  • Emails can only be read online, some clients store copy for offline access

  • Provides helpful features such as folders

  • Can be access from any client

Email privacy

• Email is not secure means of communication

• Can be intercepted, server admin can read, employees have right to read your emails

• Email encryption such as PGP or 2FA

Blogs

• Short for web log

• Website where posts are displayed in reverse chronological order

• Different kinds: photo, video, audio

Microblogging

• Form of broadcast communication similar to blogging

• Key difference: smaller portions of content are shared

• E.g. Twitter, Instagram, Pinterest

Wikis

• Set of webpages that can be edited by anyone - encourages collaboration

• Written in plain text with wiki markup used to add formatting

Advantages & Disadvantages of Wikipedia

Advantages

• Everyone can access and contribute

• Easy to use

• Quick to develop material

• Vast amount of information available

Disadvantages

• No direct quality control

• Bias in some articles

• Information changes rapidly

• Vandalism

  • Bots, recent change patrol, watchlists and reporting system to counter

Wiki Markup

• New line ignored while blank line creates new paragraph

• Headings use =, 4 levels

• Italics and bold: same as md but uses ‘‘ and one more than *

• Links:

  • [[name of page]], [[name of page | label]]

  • URL, [URL label]

• Lists:

  • * for unordered

  • # for ordered

Packet-switching Network

• Data is broken into packets, which are then sent on optimal network route

• Each node on route sends packet onto next destination, avoiding congested/broken nodes

Network Hardware

• Switch

  • used to connect multiple devices to the same network

• Router

  • Directs traffic around network and connections networks together

• Modem (modulator/demodulator)

  • Transmitting (modulating) and receiving (demodulating) data on physical medium

Protocols

• Standardised method of communication

• Ensures send and receiver can communicate properly

• Defines:

  • Format

  • Order of messages sent and received

  • Actions taken on message transmission, receipt

• Common protocols:

  • TCP: reliable data transportation (checks data packets are received in correct order)

  • UDP: less reliable but faster

  • HTTP: client/server communication such as transferring webpages

  • Many protocols defined in RFC (Request For Comments) documents

IP Addresses

• Every host on internet needs IP

• v4:

  • 32-bit

  • 2^32 addresses

• v6:

  • 128-bit

• DNS (Domain Name System) converts IP to domain name

• DNS servers perform translation between IP and URL

Client and server software

Client Software

• Web browsers

• Email clients

Server Software

• HTTP servers

Fibre Cables

• High capacity fibre optic cables laid on land and under sea

• Companies rent out capacity

• Connects countries together to form global internet

Cloud Computing

• Model for enabling convenient on-demand access to shared pool of configurable computing resources

• Resource pooling, reliability, reduced costs, measured service, rapid elasticity

• Service Models: IaaS, PaaS, SaaS

• Deployment Models: public, private, hybrid

Virtualisation

• Partitioning of resources of a physical system e.g. VPS

• Key enabling technology of cloud computing

• Allows multiple VMs to run on same physical system

WWW

• Webpage: document on WWW access through web browser usually

• Website: collection of webpages

• Web browser: application software used to access content on WWW

• Web server: computer with software that makes files available on WWW

URLs

• Uniform Resource Link

• Protocol: https

• Domain: knowt.com

• Path on server: flashcards/da818659-062e-414c-8701-62426d3dbae8

• Resource: edit

HTTP/HTTPS

• HyperText Transfer Protocol

• Used by web browsers to request resources from web server

• HTTPS:

  • Encrypts HTTP connection with TLS (Transport Layer Security)

Other parts of WWW

• Proxy: between client and server to intercept and process requests

• Cache: stores recently requested resources to be access quickly

• Firewalls: prevents unauthorized access to private network

Client → (proxy → cache) → firewall → server

Search engines

• Website that helps user search for content on WWW

• Indexes content on web (indexing), used to build list of results based on search terms input by users

• Uses spiders (web crawling) to scan pages on WWW, spiders are programs that follow links and gather information from webpages

• Search engine’s index updated with information gathered by spiders

Filter Bubble

• occurs when search algorithm offers personalised results, limits diversity of information presented to user

• can help people find relevant information

• risks isolating people within their own bubble of information