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What is the purpose of the CPU?
To process data and instructions by constantly repeating the FDE cycle
What are the steps of the FDE cycle?
Fetch - causes the next instruction and any data involved to be fetched from main memory
Decode - decodes (understands) the instruction
Execute - the instruction is executed (processed/carried out)
The process/cycle is then repeated
What is the function of the control unit?
to direct/coordinate the CPU’s operation such as the timing of other CPU parts
receives signals from the system clock and sends timing signals and control signals to other CPU parts such as RAM and ALU
to decode and execute instructions
What is the purpose of the ALU?
to carry out arithmetic calculations and logic operations
What is the purpose of the PC?
to hold the address of the next instruction to be executed
incremented by 1 as soon as that instruction has been fetched
What is the purpose of the ACC?
to temporarily store arithmetic and logic results from the ALU
What is a register?
a temporary storage place for one instruction or address
What is the purpose of the MAR?
To copy and hold the address of the instruction to be executed from the PC
What is the purpose of the MDR?
To fetch the instruction at the address in MAR from memory and to copy it to the MDR where it is held
the CU will decode that instruction and decide of any data needs to be fetched
if so, the MAR holds the address of the data
the data is fetched and copied to MDR
What are the key features of Von Neumann architecture?
program instructions and data the programs are using are both stored in the same memory
CPU accesses both instructions and data from the same RAM
What is clock speed?
everything in the CPU is coordinated by the pulse of an internal clock
The number of FDE cycles run per given
time/second
the default clock speed is 3.5GHz meaning it can process 3.5 billion instructions per second
How does clock speed affect CPU performance?
the faster the clock speed, the more FDE cycles are completed so more instructions are processed per second and a better performance
overclocking - increasing the clock speed higher than the recommended rate. leads to faster performance but also overheating and damage to the machine
underclocking - decreasing the clock speed lower than the recommended rate. leads to slower performance but will increase the lifespan of the machine.
What is a core?
a complete set of CPU components and each can perform its own FDE cycle
multicore CPU has more than one of the same components in the CPU
How does the processor speed and number of cores affect CPU performance?
one cycle per second = 1Hz = 1 instruction per second
CPU can only execute 1 instruction at a time
in theory, dual core processor has the potential to execute 2 instruction at a time and a quad can do 4
however this is only under ideal conditions such as a program that has been designed to work with multi core processors
if one core is waiting for another core to finish processing or the software used is not written to make use of multi cores, the performance may not increase
What is cache memory?
small amounts off very fast and expensive memory in the CPU
used for frequently and recently accessed data
How does cache memory affect CPU performance?
faser to access as it is closer to the CPU than RAM so it can provide data and instructions at a faster rate
useful if there is a while loop in a program - storing all the instructions in cache speeds up execution
computer with more cache has a faster performance - repeatedly used instructions can be accessed quicker
costly so most computers only have a small amount
in most systems, level 1 is used 50% of the time and level 2 is used 90% of the time - reduces the time the CPU has to wait
What are the features of level 1 cache?
extremely fast but small
2-256KB
located on the CPU
each core will have its own level 1 cache
What are the features of level 2 cache?
very fast but slower and bigger than level 1
256KB-8MB
located on the CPU
usually also given to each core
What are the features of level 3 cache?
slowest and biggest cache but still faster and smaller than RAM
4MB-50MB
located on CPU and shared between all cores on the processor.
What is an embedded system?
a small computer sysem built into a larger machine or device to provide a means of control
is a combination of hardware and software
What are the features of embedded systems?
single microprocessor
programs stored on ROM
performs specific and limited pre programmed tasks
used to control a device with simple inputs
one purpose - cannot install new software
typically very reliable - low risk of bugs developing
slower CPU speed than general purpose
They tend to require less power. Some devices run from batteries.
What are some examples of embedded systems?
washing machine
dishwasher
traffic light
electronic calculators
GPS
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What are the features of primary storage?
very quick because it is directly accessed by the CPU
typically smaller in storage size
known as main memory
includes RAM and ROM
Why do computers need primary storage?
primary storage is low capacity internal storage that can be directly accessed by the CPU
program instructions and data must be copied from the hard drive into RAM to be processed by the CPU as primary storage access speeds are faster than secondary storage devices
What are the differences between RAM and ROM?
RAM
can be read from and written to
volatile - loses data when power is off
CPU can access any part of the memory in the same amount of time
typically 4GB-32GB
ROM
can be read from but not written to
non volatile
typically 4MB-8MB
What is the purpose of RAM?
stores at any one time
the part of the operating system currently in use
the software or part of it currently in use
the data which the software is using
What is the purpose of ROM?
used to store
the bootstrap - the initial program that is run which gives the instructions of where to find the OS on the hard drive
the BIOS which controls the processor speed and system time
What is meant by virtual memory and how does it work?
a part of the hard drive (HDD) used as an extension of RAM
used when there is insufficient space in RAM
if new data is needed to be stored in RAM, unused data in RAM is moved to the hard drive so new data can be transferred to RAM
What are the advantages and disadvantages of virtual memory?
advantages
uses cheap secondary storage on the hard drive
- prevents “out of memory” error message - files and programs will still open
allows programs to run simultaneously
disadvantages
accessing virtual memory is slow - existing data in RAM needs to be copied to the virtual memory and then the data in virtual memory needs to be copied to RAM when in use
What are the features of secondary storage?
slower because it is not directly accessed by the CPU (not directly embedded on the motherboard and can be external)
typically larger in storage size
used for long term storage of files
includes magnetic, optical and solid state storage
How does magnetic storage work?
a read/write drive head moves nanometres above the disk platter and uses the magnetic field of the platter to read or write data to it
What are the features of magnetic storage?
tracks - concentric circles, each of which are divided into sectors
drive heads mounted on mechanical arms read and write data
500GB-12TB
What are the advantages and disadvantages of magnetic storage?
advantages
large capacity
cheaper cost per gigabyte
faster access speed than optical storage
disadvantages
not durable due to moving parts that will eventually fail
not portable when powered on - in a sealed unit for precision and moving can damage the device
slower access speed than solid state
noisy
need to defragment
How does optical storage work?
laser projects beam of light onto a spinning disk
What are the features of optical storage?
data stored as pits and lands pressed into a spiral track circulating outwards from the centre
laser passes over and measures the reflection, derviving 0s and 1s from this
CD ROM up to 720MB
DVD (dual layered) up to 8.4GB
Blu Ray (dual layered) up to 50GB
What are the advantages and disadvantages of optical storage?
advantages
cheap - especially in bulk
portable - thin and lightweight
disadvantages
low capacity compared to other storage types
not durable - fragile, can break and scratch easily
slowest access speed
How does solid state work?
data is recorded onto solid chips without any moving parts
large electric current is used to force electrons through a barrier and trap them on the other side
they remain on the other side until flashed with a new current
What are the features of solid state?
uses non volatile flash memory to store data
does not have mechanoical movng parts
100TB -16TB
What are the advantages and disadvantages of solid state?
advantages
medium capacity
usually durable and reliable - no moving parts
portable - small physical size
fastest access speed - no moving parts
require little power
less noisy
disadvantages
more expensive cost per gigabyte
cheap usb can snap or break
limited write/rewrite cycles
What are the uses of magnetic storage?
PCs
storage of large amounts of data
back up
archiving
What are the uses of optical storage?
multimedia storage
back up
archiving
What are the uses of solid state storage?
higher end laptops
smartphones
cameras etc
Why must data be converted to a binary format?
computers are comprised of many transistors which are tiny switches
these only have 2 states - on (1) and off (0)
so all data must be represented in this way to be processed
What are the units of data storage?
bit - the smallest unit - a single 0 or 1
nibble - 4 bits
byte - 8 bits
kilobyte - 1000 bytes
megabyte - 1000 kilobytes
gigabyte - 1000 megabytes
terabyte - 1000 gigabytes
petabyte - 1000 terabytes
How to calculate image file size?
colour depth x image height x image width
How to calculate text file size?
bits per character x number of characters
How to calculate sound file size?
sample rate x duration(s) x bit depth
What is binary?
a base 2 number system
only two possible values - 0 and 1
What is hexadecimal?
a base 16 number system
16 possible values - 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F
used as short hand to binary because it uses fewer characters to write the same values, making it less prone to errors when reading or writing it - easier to understand
used in MAC addresses and for representing colour values
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What is compression?
to make a file smaller in size
Why is compression used?
files take up less storage space (so more files can be stored)
files can be transferred quicker (because they are smaller)
files can be read from or written to quicker
What is lossy compression?
some data (which cannot be seen or heard by humans) is removed by an algorithm from a file to reduce its size
further lossy compression will remove data that humans can see or hear, negatively affecting the quality
data is completely lost once removed - can never get back original file
What is lossy compression commonly used for?
images, audio and video, for example to send over the internet
What is lossless compression?
reduces the size of a file by using Run-length encoding (RLE) which looks at data in a file for consecutive runs of the same data. These are stored as one item of data instead of many
no data is removed permenantly and file can be returned to its original form when decompressed
no quality is lost but doesn’t reduce file size as much
What is lossless compression commonly used for?
files that would be useless if data was removed - executable files and word documents
What is a LAN?
local area network
a network over a small geographical area such as a single site
the network infrastructure is usually owned and managed by the organisation
What is a WAN?
wide area network
a network over a large geographical area such as multiple sites, towns, cities countries or continents
requires third party connections such as phone lines and satellite
What is the role of a client in a client-server network?
a less powerful computer that relies on servers to provide and manage data
they have no control over the network as a whole or over individual computers
to send requests to a server, wait for a response, and then receive the response
What is the role of a server in a client-server network?
a more powerful computer that manages and stores files (provides services) to other computers on the network
to wait for requests from clients, to perform the request and to send a response back to the client
What are the advantages and disadvantages of a client-server network?
advantages
can be controlled centrally from the server which also backs up all software and file servers as well as controls security
hardware, software and resources can be shared across the network (e.g printers, applications and files)
allows for improved scalability - more clients can be easily added to the central server
disadvantages
large amounts of traffic congestion will cause it to slow down
all users are reliant on the central server so if there is a fault with it, the whole network will fail and if a back up has not been made to a back up server, all files will be lost
servers are expensive
hard to manage and maintain - IT technicians needed
malware can spread quickly across the network
What are the roles of computers in a peer to peer (P2P) network?
there is no central server so data is shared directly between systems and all computers have equal status
each requests and performs tasks on the network - serve each other
all responsible for providing data
What are the advantages and disadvantages of a peer to peer network?
advantages
simpler and cheaper to set up than client server - no dedicated equipment like a server needed and no specialist staff
direct communication - optimal for quickly sharing files between systems, especially media files
computers are not dependent on a single server
if a computer goes down, only its files are lost
disadvantages
no central device to manage backups or security so it must be performed on each individidual computer - less secure
decreased scalabilty and ability to manage beyond a few computers
files on individual computers may be hard to locate as each user is responsible for their own filing so it may be unorganised
if a computer is switched off, the data can’t be retrieved at all.
computer performance will decrease with more connected devices, especially if those are slow
How does bandwidth affect network performance?
it is the max amount of data that can be transferred through a connection at a time
bandwidth of the medium is shared between all connected devices
as the number of devices increases, bandwidth per device decreases so the network is slower
How does latency affect performance?
the length of time a packet of info sent from one device takes to travel through the network to another device (delay in receiving it)
a higher latency slows the network performance
How does the number of collisions (error rate) affect network performance?
when devices try to communicate with each other at the same time, the signals collide
the transmission fails and the signal must be re sent which slows the network
What are all of the factors that affect network performance?
the bandwidth available
number of users at the same time
number of data collisions
latency
interference
distance to trravel/signal strength
amount of data to transfer
applications being used
server/CPU performance
When is a client-server network used?
best suited to organisations with many computers, or to situations where many computers need access to the same information. Many schools use this type of model.
When is a peer to peer network used?
best suited to smaller organisations that have fewer computers, or where fewer computers need access to the same data.
What is the role of a wireless access point?
to povide a link between wireless and wired networks
creates a wireless LAN that allows wifi enabled devices to connect to a wired network
e.g a wifi or bluetooth hotspot
may be a seperate device or built into another device such as a router
uses a a radio transceiver
What is the role of a router?
to transfer data packets between networks
receive data packets and use the IP address in the packet header to determine the best/most suitable route for transmisssion (quickest and shortest)
data is transferred from router to router across the internet towards the destination
it stores the IP address of each computer connected to it
What is the role of a switch?
to connect devices together on a LAN
recieves data packets from a connected node, reads the destination address in the packet header and forwards the data directly to its destination
generates a list of the MAC addresses of all devices connected to it when it receives data
scans for a matching destination address before sending
What is an alternative to a switch?
hub
forwards a copy of the received data to all connected nodes
less secure
slower - unneccessary signals are sent
What is the role of a network interface controller/card?
internal piece of hardware (embedded on the motherboard) required for a device to connect to a network
includes a MAC address which is used when sending data across a LAN
ethernet cable plugged into it to allow data to be exchanged between the device and the network
What is transmission media?
the communication channel along which data is transferred
carries data signals
can be wired or wireless
type used afffects performance
What are the advantages and disadvantages of copper cables?
use electricity
advantages
tried and trusted technology
relatively inexpensive
disadvantages
signal affected by electric
and magnetic fields
low bandwidth
heavy cables
What are the advantages and disadvantages of fibre optics?
use light
advantages
very fast data transmission
low loss of signal over distance
not affected by magnetic or
electric fields
require very little power
more difficult to intercept than copper cables
disadvantages
high investment cost
need for expensive optical
transmitters and receivers
What are the advantages and disadvantages of wireless
transmission?
uses radio waves
advantages
allows devices to be used
anywhere provided there is a
signal
no need for trailing wires (safer)
easier to add devices to a
network
disadvantages
data transmission rate less
than that of wired systems
signal can be blocked by
objects or walls
increased risk of security issues
What is a network topology?
the layout of computer systems (nodes) on a LAN
star and mesh
What is a star topology?
nodes are connected to each other through a central switch through which all communication passes
What are the advantages and disadvantages of a star topology?
advantages
improved security - data packets sent directly to and from the switch in the centre and not necessarily all devices
new nodes can be added directly and easily to the central switch - network will not need to be shut down to modify it
if an attached node or cable fails, the rest of the network is not affected
faster data transfer speeds - data goes to intended recipient with minimal collisions - higher performance
disadvantages
requires additional hardware which is expensive and needs to be maintained
single point of failure - if the central device fails, the whole network will become unusable until fixed
What is a mesh toplogy?
no central connection point - each node is connected to at least one other node
each acts as a router to relay data
full mesh - each node is connected to every other node
What are the advantages and disadvantages of a mesh toplogy
advantages
if one cable or node fails, the data packets can take an alternative route - no single point of failure
many possible connections allow data transmission from multiple devices simultaneously - can withstand large amounts of data traffic - messages more likely to get through and do so quickly
modification and expansion can be done without disrupting the entire network
disadvantages
large amount of cabling needed in a full mesh especially - expensive to install and maintain - difficult to maintain
may involve redundant connections (those that will never be needed)
Where is a star toplogy found?
smaller businesses
schools
wireless home networks
Where is a mesh toplogy found?
large organisations that require reliable communication
e.g military or emergency services
What are the advantages anmd disadvantages of using networks over having stand alone computers?
advantages
file sharing
hardware sharing
communication - email, chat, video etc
roaming access - users can sign in to any computer on the network and be able to access their files
on larger networks (businesses and schools)
centralised maintenance and updates - network managers can apply software updates across a network, removing the need for individual users to do it
centralised security - anti-virus software
and firewalls can be implemented across a network, helping to protect user files from risks
user monitoring
levels of access - different users can be given different access rights.
disadvantages
cost - additional equipment is needed
require management by technical staff
malware can easily spread across an improperly secured network
hacking once a device is connected to another device, it is possible that data may be accessed without the device owner's permission
What is the internet?
a worldwide collection of interconnected computer networks
What is web hosting?
a service offered by companies that will host web pages and files
a website must be hosted (stored) on a web server to be able to be accessed by others on the internet
How does web hosting work?
a web server responds to the web browser (client’s) request to display a web page
the web server processes the request by preparing the web page and then returning it to the web browser
it is then displayed to the user
What are the advantages of web hosting?
advantages
web hosts have far more bandwidth - can serve more users
able to monitor their equipment 24/7
web hosts will back up sites remotely
What is the domain name system?
every web page has a domain name that is easy to remember and type in as well as a unique IP address for the device that the web page is stored on
a DNS server stores a list of domain names and a list of corresponding IP addresses
13 DNS root servers worldwide - complete list of all domain names annd their IP addresses
What are the steps taken to display a web page?
a domain name is typed into the address bar of a browser
a query is sent to the local DNS server for the corresponding IP address of the domain name
it will check if it holds the corresponding IP address. if it does, it passes it to your browser
the browser them connects to the IP address of the server and accesses the website
if the local DNS server does not hold the IP address, the query is passed to another DNS server at a higher level
if found, the address is passed down to servers lower in the hierarchy until it passes the local DNS server and then your browser
What is the cloud?
a network of servers accessed on the internet
example of a remote service provision
software as a service
purposes include running applications, storing data and processing
data stored on large servers owned by a hosting company
What are the advantages and disadvantages of cloud storage?
advantages
huge capacity and ability to upgrade your subscription for more storage
free for a certain amount of storage
access can be granted to another user and people can work on a file simultaneously
can be accessed from anywhere on demand with an adequete internet connection
no need for a powerful computer to store data
back ups are supposed to be done by the service provider
disadvantages
unusable without a good enough internet connection
no guarantee that data is being backed up
personal data will be stored on another company’s servers - data protection risk
Wired connections use physical cables (copper or fibre optic) and requires a NIC. They use a wired connection protocol - usually ethernet.
What are the advantages and disadvantages of wired connections?
advantages
higher data transmission speeds
higher maximum distance for reliable communication
more secure - physical connection would be needed to intercept data
disadvantages
require more space
expensive and harder to install - require technical knowledge
restricted movement
Wireless connection (wifi and bluetooth) use radio waves and require a WNIC.
What are the advantages and disadvantages of wireless networks?
advantages
cheaper and easier to install - home wifi networks - automatic
freedom of movement
disadvantages
slower speed - signal affected by the node’s distance from the wireless access point as well as any obstacle
lower maximum distance for reliable communication
less secure - signal cannot be contained so data can be intercepted without authorised users knowing
When would a wired network be most suitable?
if the devices are unlikely to need to move
When would a wireless network be most suitable?
if the devices are likely to need to move
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