Hardware and communication Flashcards
paper 2
optical character recognition (OCR)
converts printed media into editable text documents using a scanner - allows you to change text on a printed document ( eg books)
optimal mark recognition (OMR)
based around a predefined form with areas where someone can mark multiple choice responses. scanner detects dark marks on page and notes position of them
(used for exams)
magnetic ink recognition (MICR)
uses in containing iron oxide and specific fonts so data written in the ink can be read by MICR reader - used for cheques so that only relevant text it scanned.
OCR problem
can be read wrong by the computer so must be proofread
OMR problem
if mark not dark enough or large enough, scanner may miss it
resistive touch screens
cheaper + made up of 2 thin transparent sheets
when pressure is applied the sheets touch each other and a voltage is recorded in that position
resistive touch screen problem
don’t provide as sharp of an image as capacitive screens and don’t allow for multiple touches at once
capacitive touch screens
more expensive but allows clearer image and multiple touches at once
utilise the fact the human body conduct electricity so when you touch screen you change electric field of area you touched - this is registered as a click and X,Y coords are sent to OS
capacitive touch screen problem
doesn’t work when wearing gloves or using item to touch screen.
voice input
microphone detects voice commands which will be interpreted by computer and carried out
voice input problem
set amount of commands that the computer is able to understand and carry out.
vocabulary dictation
users speak into microphone and computer tries to translate into text
vocabulary dictation pros
can be faster than keyboard input
reduces spelling mistake risk
hands free
vocabulary dictation cons
background noise interferes
speech impediment, strong accents etc won’t be understood as well
words that sound the same may be misinterpreted.
voiceprint recognition
process of capturing person’s voiceprint, digitising and storing the data on computer system
used in security systems by comparing voice prints
secondary storage (backing storage)
non-volatile, long term storage that is not directly accessed by CPU.
stores data not actively being used and takes longer to retrieve from SS than from memory
computer uses input and output channels to transfer data from secondary to primary storage when needed for processing
types of secondary storage media
optical storage (CD/DVD/Blue-ray)
magnetic storage
solid stage storage
optical storage
laser beams projected onto disk and if light is reflected then data is read as a 1 if not it’s a 0
magnetic storage
eg hard disk drives (HDD)
data stored using a read-write head and magnetic platter (disk)
good compromise between storage capacity, performance and cost
solid state storage
eg solid state drive (SSD) or flash drive
no moving parts, data stored on flash memory chips
has low power consumption and high speed access but more expensive than HDDs
RAM can retain its state after power disconnected
fragmentation
over time files split and stored on different parts of the disk -stored in non-sequential manner
takes longer for disk heads to move between parts of the file
defragmentation
files are physically rearranged on the disk so they are no longer fragmented and parts of each file are stored together. SSDs cannot be defragged
HTTP
hypertext transfer protocol
transfers images, videos etc over internet
FTP
file transfer protocol
transfers files across internet between client and server
often used for large files
SMTP
simple mail transfer protocol
send and receive messages
TCP/IP
transmission control protocol/internet protocol
group of protocols that control how data is broken down for transmission from sender to receiver - includes error checking
IMAP
internet messaging access protocol
after SMTP directs email to correct server IMAP allows it to be retrieved on a device
DHCP
dynamic host configuration protocol
ensures each device connected to a network has a unique index (IPAddress)
UDP
user datagram protocol
sends data across internet but without handshaking or error checking so it is quicker
used for live streaming especially gaming
handshaking
signal sent from once device to the other in order to agree on a set of protocols to use before data is transferred
computer network
a collection of interconnected computers that have the ability to communicate with one another either through wired (ethernet) or wireless (wifi) connections
can be a LAN or a WAN
peer to peer network
no computer acts as a server - all computers must work together to fulfil the required task (broken down and split between computers)
known as distributed processing
protocol
set of rules that governs communication between devices
network interface card
responsible for placing packets onto network cables in form of electronic signals (or light bursts if cable is optical)
electric signals depend on physical protocols being used on network
hub
packet sent to hub where it will be broadcasted to all other computers connected to hub
the more PCs connected = more traffic thus more collisions and corrupted packets
switch
perform routing of packets from one port to another
when packet arrives switch determines which port has destination address (known as routing)
routes at the MAC address level rather than IP level
MAC address
when packet arrives at a switch, it looks at the MAC address and forwards it to correct port
routers
- connects different segments of a LAN together
- allows access to outside networks (WANs) eg the internet
- routes based on IP address - sections of network can be assigned similar IP address ranges which provide router with more info to direct packet.
- more powerful processor + is more expensive than switch as has to deal with more devices
wireless access point (WAP)
device that allows wireless devices to connect to a wired network . WIC connects to a WAP
wireless network security
can detect wireless network by sitting close by so security is high priority
use encryption and require special key in order to stop unauthorised users.
wireless network issue
distance from the router, interference from other devices, bad weather etc can impact speed and quality of connection.
low wireless signal can cause packets to contain errors meaning data needs to be resent.
components of Von Neumann computer system
arithmetic logic unit
control unit
registers
buses
cache/internal memory
arithmetic logic unit (ALU)
processing of data as a result of arithmetic and logical operations
result stored in accumulator
control unit (CU)
manages fetch/decode/execute cycle fetches each instruction in sequence, decodes and synchronises it by sending control signals to other parts of computer
registers
eg MAR, MDR, CIR
a small, fast access temporary storage
cache memory
small very fast memory placed near processor
can be accessed by CPU more quickly than RAM to execute frequently accessed instructions
when cache is full, least recently used data is discarded
address bus
used to transmit addresses in RAM of next line of program code to be fetched or an input/output port where data is to be stored or loaded
data bus
used to transfer program code between RAM and processor or input/output ports
control bus
send control signals from processor to RAM memory or input/output ports to initiate data transfer
carries interrupt signals to processor to indicate hardware/software requires attention
Von Neumann pros
as CU retrieves data and instruction in same manner from one memory, design and dev is easier and cheaper
memory organisation allows them to utilise memory’s whole capacity.
Von Neumann cons
parallel implementation of a program not allowed due to sequential instruction processing
Von Neumann bottleneck - instructions can only be carried out one at a time and sequentially (can be minimised using cache memory)
registers in FDE cycle
accumulator
memory address register
memory data register
program counter
current instruction register
accumulator (ACC)
register that holds the results from the ALU
memory address register (MAR)
either stored mem address of data to be fetched or address of data that has been fetched
memory data register (MDR)
holds data after fetch cycle
acts as a buffer holding data until processor is ready to use it
program counter (PC)
stored address of next instruction to be executed from memory
will increment at end of each task
current instruction register (CIR)
holds instruction that is currently being executed.
fetch, decode, execute cycle process
- PC contains address of instruction to be fetched
- address bus used to copy contents of PC to MAR
- instruction at that location copied to MDR temporarily
- contents of MDR copied to CIR
- value in PC incremented by 1 so next instruction can be fetched
- instruction decoded then executed sending out control signals to memory and input/output devices
opcode
binary representation of instruction given to a computer
operand
specifies the data to be manipulated
parallel processing
multi-core systems that can split a task up into threads and processes it each thread simultaneously
parallel processing pros
more instructions processed in shorter time
tasks can be shared to reduce load one each processor and avoid bottlenecks
parallel processing cons
hard to write programs for multi-core processors
results from each needs to be combined at the end which adds to time taken to execute
not all tasks can be split
multiplexor
allows multiple messages to be combined so they can be sent over a data link simultaneously
time division multiplexing
allocates small time slices alternately for data from each of the input message streams
frequency division multiplexing
sends diff messages simultaneously but using different transmission frequencies
