Computer Systems Flashcards
Computer System
System is a combination of many connected parts all working together to achieve a common goal
Computer system involves interaction between hardware, software, data, and the user
Can be made up of multiple computers or programs
System becomes more complicated when connected to internet, more interaction
Computer Architecture
Specification of how a computers different parts are physically, and logically, laid out or connected
No single design, engineers have a great deal of freedom when designing computers
Designs evolved greatly over the years, most common is the Von Neumann architecture
Von Neumann Architecture
Central Processing Unit – processes (carries out or executes) instructions
Memory which stores data to be operated on, instructions (programs that operate on) data and the results
A bus connects the CPU and memory
Input and output devices that allow data to come into the computer and results to be sent out
CPU (Central Processing Unit)
CPU or processor carries out computations on data by following instructions, resulting in an output
Contains control unit, Arithmetic/logic unit and registers
Modern CPUs contain billions of transistors
Control Unit directs the operations of the CPU
ALU is where arithmetic and logical processing takes places. Receives instructions and data and operates accordingly
Contains registers
Registers
Registers are temporary storage locations (memory) that the CPU can access quickly, when carrying out operations on data
Program counter is type of register, keeps track of where CPU is in the program sequence and indicates what is next
Memory
RAM and ROM
RAM (Random Access Memory) – temporary memory, holds data and instructions of program currently being executed. Volatile memory; computer loses power, data is lost, typically fast
ROM (Read Only Memory) – non-volatile. Contents remain stored regardless of whether computer is powered on or off. Typical use is BIOS – small amount of ROM that is used to store the computers start-up routines
RAM and ROM are both types of primary storage. This is used to store information for immediate use by CPU
Fetch-Execute Cycle
As CPU processes instructions, it runs through same cycle over and over again
CPU fetches the programs next instruction from memory
Instruction is found at a memory address and is stored in binary code
CPU decodes the binary code revealing an instruction which is executed
CPU may need to use some of the registers to store information while executing the instruction
After last step is completed, cycle starts again, and this happens millions of times per second on modern computers
The Clock
Operation of CPU and other components in computer must be timed very accurately to ensure all step-by-step instructions are perfectly synchronized
Clock generates a signal consisting of a continuous stream of electrical pulses at a very stable frequency
Pulses are fed to all circuits in the computer system to ensure they operate together with the right timing
Factors Affecting Speed of CPU
• Clock
o Main factor is the clock speed
o Each pulse from clock means the CPU fetches and executes one instruction
o 5 gigahertz is 5 billion instructions per second
• Cores
o Parts of the CPU that can execute instructions simultaneously
o If CPU has 8 cores, can carry out 8 instructions during one clock cycle
• Cache
o Size and speed of the cache can affect performance greatly
The Bus
Connects the CPU and memory
Collection of wires that allow data and instructions to move from memory to the CPU and back
Computer typically has more than one bus, only one between CPU and memory
Communication channel that carries data between internal computer components
Input and Output Devices
Pieces of hardware used by a human user or other system to communicate with a computer
Input devices – keyboard, joystick, scanner, barcode scanner, mouse
Output devices – screen, speakers, printers, headphones
Input and output devices – Touchscreen, DVD, webcam, USB, secondary storage
Apart from CPU, memory, and bus, all other parts in von Neumann architecture are inputs or outputs
Secondary Storage
Devices used to store data persistently.
Non-volatile, store info regardless of whether the computer is on or off
Data can be used at any time.
Slower and cheaper than primary storage but generally larger than primary
Can store several terabytes today
Hard drives are widely used
Magnetic hard drives consist of a platter that rotates at a very high speed and a head that moves across and reads information
Solid state disks (SSD) are faster and more durable as they have no moving parts and are usually more expensive
Motherboard
Circuit board that devices (CPU, main memory, hard drive, input output devices) are physically mounted on – soldered on or plugged into
When plug USB into computer, physically connecting to the motherboard
Circuit board contains a non-conducting fiber material with several layers of interconnecting paths that act as wires, connect various components which are on/plugged into motherboard
Ports are also connected to the motherboard (USB ports) that allow to connect inputs and outputs
Sometimes components connected to daughter boards which are connected to motherboard
Binary Code and electrical signals
Modern computers use binary code to represent all information, represented by symbol pairs (0,1)
Referred to as on (signal present) and off (no signal present)
Electricity –
form of energy arising from the movement of electrons
Electrons –
charged particles that are found inside every atom
Electric Current –
flow of electrons from one place to another, greater rate of electron flow, greater the current is
Voltage –
The pressure from an electrical circuit’s power source that pushes charged electrons through a conducting loop (can be used to illuminate a light)
Resistance –
Measure of difficulty of passing an electric current through a material. The more resistance, the less electricity will flow. (Copper has low resistance, glass has high resistance)
Transistors –
Tiny electronic switches that allow a small current change to switch on or off a larger current
Resistors
Device that reduces current flow
Typically achieved by passing electricity through a material whose resistance does not allow for electricity to flow efficiently
Resistors have different values. Different coloured bands on them indicate values
Capacitors
Stores electrical energy in the form of electric charge for short amount of times
Often used in volatile memory (RAM) in computers
Capacitance is a measure of the amount of charge that a capacitor can store
Used in touchscreens – Skin is weak electrical conductor, touches a screen changes the amount of charge at point of contact
Operating System
Collection of programs that control the operation of a computer, application programs (Microsoft Word, Excel, Chrome) and any attached devices (keyboard, mouse, printer)
Runs all the time in the background while the computer is switched on
PCs (windows), Macs (Mac OS X), Smartphones (Android and Apple iOS)
•Functions:
o Managing how data is received from input devices and sent to output devices
o Managing how computer interacts with other computers
o Controls where programs and data are located in computers memory
o Provide interface between user and computer to allow the user to interact
o Manage files on computer
World Wide Web
System (or network) of connected files hosted on the Internet that can be searched or browsed
Can include pages, pictures, video, sound, and other file formats that can be searched and browsed
These are all connected using hyperlinks, all websites put together is the World Wide Web
Uses the internet as a transmission medium, needs the internet to work
The Internet
1969, two computers in UCLA communicated with each other, beginning as was real-time connection
Internet is a global network of networks consisting of billions of connected computers and other devices
Theoretically, can all communicate with each other in different ways – copper wires, fiber optic lines, wireless satellite, undersea cables
Network of connected computers, i.e., the Internet is the network
Internet of Things
Interconnection via the Internet of computing devices embedded in everyday objects (TVs, Cars, Fridges) enabling them to send and receive data
Client-Server Model
Visit a website, computer issues a request that goes to the appropriate server
Server then carries out that request and the information representing the web page is transmitted to computer
Browser renders it to a web page
Client requests resources, server provides them
Server can become overwhelmed when many clients make requests at same time (concert tickets)
Communication Protocols =
Set of rules describing how to transmit data across a network (can be the internet)
• Http
Hypertext Transport Protocol
(sometimes shown at start of web address)
Operates at the application layer
Request response protocol, allows client to issue request for resource and server responds with data
Protocol is specific to applications (programs)
Https
Hypertext Transfer Protocol Secure
Secure version of http
Data transmitted between client and server is automatically encrypted
Messages do not make sense without encryption key which client and server should have
Standard on the web, mainly for online payments
• TCP
Transmission Control Protocol
o Operates at transport layer
o Ensures that binary information is transported reliably between computers
o Info is broken up into packets for efficient routing
o TCP keeps track of packets, ensuring they remain free of error and arrive to client in same order as was transmitted
IP
o Internet Protocol
o Operates at the network layer
o Handles creation of data packets and how they are routed around the network to their destination
o Done using IP addresses (code that identifies a computer network or particular computer or device, unique for every computer on Internet)
o IP ensure that correct IP address is attached to every packet of data so delivered to right destination
TCP/IP
Often combined into one family of protocols
TCP tracks packets and ensures arrive error free
IP governs creation of packets and their addressing and routing across the network
WiFi
o
•
Radio wave technology that allows devices (phones, laptops, TVs, printers) to communicate with each other and to access the Internet wirelessly
o Operates at the physical layer
o Manages the flow of data around a WiFi network
VOIP
Voice over Internet Protocol
Number of methods which are designed to deliver voice data (and video) over Internet
Facetime, WhatsApp, Skype all use VOIP methods
Gateways –
connect networks with different protocols
Routers –
Forward data packets between computer networks (between internet and home computer)
Network bridges –
Create single network from multiple network segments
Network switches -
forward data only to devices that need it
Repeaters –
receive and re-transmit data, often used in fibre optic cables to boost signal strength
Cloud Computing
Refers to storing, processing, and accessing data, programs, or services over the Internet on servers designed for these purposes
Managed and hosted by companies that provide various cloud services
Company is responsible for keeping data available, accessible, and secure
Customers pay for as much storage and processing power they require
Providers include Dropbox, Google Drive, and Amazon Cloud
Easy to share information between users and have remote access to files
Risk of security breach and need internet connection to access files
