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External Hardware Devices (Magnetic Hard Disk (HDD) (Made of... (platter…
External Hardware Devices
Barcode reader
Reads barcodes off
Cans
Packaging
Book covers
(Products) #
Barcode
Sequence of Black & White bars
More light reflects
from white then black
#
Several bars which make
up a character -> called
symbol
symbology (p. symbologies)
set of symbols allowed for
a specific barcode standard
#
Encodes info
E.g product indentifiers
#
Types/Standards #
One-dimensional
Adv. Can be decoded
easily - even at high speed
Relatively cheap
Been around for 40y
Widely used
named '1D' as a single
line (laser beam) is
traced when scanned
UPC (universal product code)
first product ever with UPC standard
10 pack chewing gum - 26/06/1974
Two-dimensional
Ex. QR codes
machine readable
markings form 2D grid
Read by CCD camera
Made of...
Light sorce
(Low-powered laser diode) #
one-dimensional barcodes
Moves over barcode diagonally
from top left corner
#
Lens
photoelectric detectors
(Photo diodes) #
reflection pattern
converted optical -> electrical form #
Reflection data
is analysed
Relative time taken the
beam spends scanning
dark/light bars - measured
Barcode decoded
-> character form (ASCII)
Look up table used
'- translate time to
corresponding char
Translated to binary digits
for computer processing
Decoder circuitry
KEY CONCEPT
To understand 'One-Dimensional Barcodes'
Digital camera
How it works
Light reflected from objects is
focussed by lens of camera
received by light-sensitive cells (photosensors)
form analogue picture
The matrix of
photosensors and
associated electronics
are either...
each cell/site gathers electric charge
proportional to the brightness of the illumination
The size of the charge per photosensor is converted from analogue -> digital using an analogue to digital converter (ADC) by the photodiodes
More processing with further filters - changed into the raw image
The raw image is then saved at the cameras specified file
Ex. Once raw image no longer needs to be adjusted - converted to JPEG
DCIM (Digital Camera IMages) - Default directory - this is on a memory card and if there is not one - it is created
Types/Standards
Photosensors
Both made from metal oxide semiconductors
with photodiodes used as photosensors
Charge-Coupled Device (CCD)
Consume 100x more power
Higher quality as been around longer
Greater light - sensitivity (less grainy)
Better resolution as packing is denser
Complementary Metal Oxide Semiconductor (CMOS)
Cheaper to manufacture
Each photosite has 1 photodiode ++ some transistors for pre-processing and so each site can be independently accessed
smaller photodiode
Are taken up by transistors receives less light - less sensitivity
Noisier images
Cameras
Cannon
Canon EOS 600D
5184 x 3456 pixels
Raw image - extention - CR2
Digital single-lens reflex cameras
Aspect ratio: 3:2
Made of...
Photodiodes
1 red 1 blue 2 green filters
(human eye more sensitive to green light)
each row contains ADC on the right
Laser Printer
How it works...
Processor in a monochrome
laser printer generates bitmap
of page in raster memory
from page description
Negative Charge is sent to the drum
Laser beams are directed
at the rotating drums surface - turned
on and off at positions
fixed by the bitmap data.
Causing negative charge to
be neutralised or reversed at the
parallel, black parts of the page
(to be printed) - the pattern of
charges is an image of the page
Charged surface is exposed
to the colourings, so that the
charged coloured/toner particles
are give negative charges so they
attach to positive charged/uncharged
areas
Raster memory stores greyscale
data for each area of page
and is used to set the voltage level #
The drum is rolled over the
paper (whilst rotating) and the
toner is transferred to the sheet.
Sometimes, to aid printing,
positive charge is used on
the back of the paper to
pull the toner from the drum
Facts
Prints whole pages
High-quality text + graphics
Page description language -
describes page to be printed
in lines/arcs/polygons
(6) Darker layers receive thicker
layers of toner - this is done
by using a higher volatage
in the gap between the drum
and toner
#
Colours/Inks
4 toners
(CMYK)
Cyan (p)
Magenta (p)
Yellow (p)
Black
Subtractive model:
Mixing all the (p) Primaries - you
get black but for a much
darker- use key (black) toner
Each toner layer stored as a indiv. bitmap
Monochrome laser printer
Prints with only black powder
& carbon black OR colouring
agents
Can only print text in black
Bad at greyscale where
small dots and varying
the arragment of the dots
(dithering/halftoning)
Radio Frequency Identification (RFID)
How it works
Uses Radio Frequencies (RF) to transmit data, timing signal + radio frequency energy (if neccessary) between reader and a transponder (ex. RFID device) - DATA CLOCK ENERGY
Reader/Interrogator & Transponder
Reader
Reader can read or read and write
Transponder
Transponder located on obj. to be identified
Has small RF antenna & circuitry for transmitting & recieving data
Types
Passive
Powered by RF energy from reader
Uses include: access control, smart labels, race timing &+
Cheaper
Less bulky
Semi-passive
powered by internal battery but still communicate w/ reader
Active
powered by internal battery
these can broadcast their own signal which is useful for tracking real-time location of obj.
larger than passive tags
have longer read range
are expensive
Storage
Have storage of few bytes - several thousand
Attached to products to keep track
When interrogated - respond
with its own unique code so
products can be recognised
individually rather than by
just its product type
ex. 12345 = green shoes (6)
12345-1 = specific pair of
green shoes (6)
Other
RFID Tag - Microchip attached to an antenna set up so it can be applied to an object (eg. clothes for sale - acting as a security tag).
Example - Smart Labels:
has with barcodes
printed on & tags
embedded in plastic
Fed through RFID printer
which prints barcode &
writes to its RFID microchip
Can be used with or without physical connection and visible contact so its possible to read a lot of codes from a distance through obstacles
KEY CONCEPT
RFID
- Any method of identifying and tracking items using radio waves; typically - a reader (aka. interrogator) communicates with a transponder (which holds digital info on a microchip OR a chipless RFID tag which uses material to reflect back some of the radio waves beamed at them)
Types/Uses
EAS (Electronic Article Surveillance)
Remove/Deactivated at till but
not read as otherwise customer
could be tracked by joining their
ID with the RFID tag serial No.
Alarms raised if stolen
1 bit transponder
Can only distinguish transponder
present and not present
Can use for stock control
RFID Smart Cards
Ex. Oyster cards
Used as tickets for journeys on public transport
Security badges
Car immobilisers
ignition key is combined
with transponder
Cat flaps + cat collars
Cattle tracking
Magnetic Hard Disk (HDD)
General
Most common form of Secondary-storage
Developed in late 1950s
Can store + retrieve large amount of data
In 2015 - Fastest rotation speed 10000 rpm
Also know as 'Block-Orientated Storage Device'
Made of...
platter
Thin, circular, made of non-ferrous metal or plastic
Coated in a fine layer of iron,
cobalt oxide or any type
cobalt alloy particles acting
as small magnets
Block
Block addresses are made up of surface address (0 or 1), track address (0 to 7,000), then a sector address (0 to 63)
Read-Write head
Spindle
Motor
Overview
Allows rapid/random/direct access to large amounts of data
How it Works
Platter is rotated at ≈10,000 turns per minute below
As the read/write head moves radially across the surface of the platter
Binary data is then recorded by the magnetic particles coating the platter aligning in one direction, to represent 0, or another, to represent 1
The read-write head moves to the specified track and waits for the specified sector to pass under it. When data is transferred from the hard disk to computer or vice versa, a whole sector is read/written.
The data is recorded, with in
concentric rings/tracks, in sectors
holding fixed number of bytes (eg. 512) -
which is the smallest unit of transfer),
on the top and bottom of the disc
Disk Buffer
Writing
Before writing to a file, it has to be opened or, if it doesn't exist, it create a new one.
This open/create action creates a disk buffer - which is linked with the file
Executing Programs do not write directly to the hard disk. It is first written to a Disk Buffer - an area of main memory (RAM).
Size of the buffer is the same as the size of the disk block. When buffer is full, the operating system writes the buffer to disk.
Reading
It is first opened, creating a disk buffer, which recieves a block at a time belonging to the file
The program which opened the file then read it from the buffer
When buffer is empty, operating system transfers next disk block (belonging to the file) into the disk buffer
Types
Whinchester Disks
contains multiple platters, on the same spindle
Sealed inside an assembly allowing disk to operate wit minimal damage & no contamination
Read-Write head built inyo assembly (one head per surface)
More platters means more storage
KEY CONCEPT
Access Time
The time interval between the moment the command is given to transfer data to the disk to main memory and the moment this transfer is completed. Made up of 3 components
Rotational Delay
The time taken for the desired sector to be directly beneath the read/write head,
Data Transfer Time
The total time taken to read the disk block and transfer it into main memory
Seek Time
The time the read/write head takes to align on the desired track
Optical Disk
Facts
The data surface contains pits in a single track 3.5 miles long!
How it Works
Binary data is recored in pits (0) and lands (1)
0 = lack of reflection when read
1 = reflection when read
reflection comes form a reflective material, usually metallic, on one of its flat surfaces
Very similar to HDD
Made of...
Label
Protective Layer
Reflective Metal Layer
Polycarbonate Disc - This is where the
data encoding
is & it's the
read side
Types
CD-ROM
Facts
introduced in early 1985
Initially used to publish encyclopaedias, reference work, professional directories, and other large databases
High storage capacity (600-700 mil bytes)
Also used for software distubution
Compact Disc - Read Only Memory
Writing
Disc-mastering machinery
Impresses pits (physical depressions) into a continuous spiral track
Reading
Disc spins at approx. 200-500 revolutions per minute depending on which part of the track is being read
Laser beam is focused onto a point in the reflective metal layer where the pits are impressed.
More laser light is reflected from the un-pitted surface than from the pitted surface
Light is detected by photodiodes, which then outputs the equivalent electrical sign
After some conditioning, result is a digital signal representing a single data bit.
This data encodes the amount of reflection as 0 or 1
KEY FACT
Flat, usually circular disc, which encodes binary data (bits) in a special reflective layer. In one form of optical disc, binary data is encoded in forms of pits (0 - lack of reflection) and lands (1- reflection) on a reflective material (usually metallic), on one of its flat surfaces.
Solid State Disk (SSD)
Facts
Newer form of secondary-storage
more efficient than HDD
Very similar to HDD
no moving parts/spinning disks
operate at a speed far above a typical hard drive (HDD)
HDD access time ≈ 10-15 milliseconds
SSD access time ≈ 25-100 microseconds
RAM access time ≈ 40 - 199 nanoseconds
Write Endurance
Write cycles - measured in number of program erase (P/E) cycles
Write endurance - Can only be reprogrammed limited amount of time until become unreliable
To prevent unreliability, wear levelling used - makes sure that all drives memory chips are used, before first cell is written on again
Used in laptops, tablets and option for desktop PC's
Lower power comspumption
Faster booting & operating system
Types
CD (compact disc)
DVD (digital video/versatile disc)
How it Works
Writing
Erases a block first before rewriting as NAND flash memory can't overwrite existing data
To alter a particular memory location, an entire block must be constructed containing the new information
Storing
Traps electrical charge, which stay there even when power is cut
trapped electrons = binary 1
absence of trapped electrons = binary 0
trapped in sites (floating gate transistors)
organised into a grid - known as a block
rows making up a block - known as a page
common page sizes; 2KiB, 4KiB, 8KiB, 16KiB
128 to 256 pages per block
block sizes; 256KiB to 4MiB
Technology
Technology used - NAND flash memory - type of EEPROM (electrically erasable programmable read only memory)
to read & write requires onboard controller contains an embedded microprocessor with RAM buffer. very important in assisting speed
Other Information
Revised
Barcode Reader
Solid State Disc
Digital Camera
Laser Printer
RFID
Hard Disk
Optical Disk
Terminology
Aspect ratio - width of image to its height
Matrix - 2D array
Noise
CR2 - File extension - TIFF specification based - Can convert to JPE
Photosite/Site/Cell - An indiv. pixel in a camera
Photodiodes # - The actual lights which allow you to view the image
Raw image - equal pixel-based digital version of an image
Bayer Filter mosaic - colour filter array - arranges RGB colour filters on a square grid of photosensors
Passive - a tag powered by te reader rather then a battery
Primary Storage - A volatile data store such as the RAM
Secondary Storage - Non-volatile storage such as Hard-Disk, Optical Disk and Solid-State Disk
Volatile - Data which is deleted/lost when the power is truned off (antonym. Non-volatile)
Non-Ferrous - all metals and metal alloys which are not/do not contain iron
radially - movement around the radius
Tracks - One if the concentric rings
Sector - Subdivision of a track, holds fixed num. bytes
Disk Block - Subdivision oof a sector
Optical Media - Discs read by lasers
COMPARISON:
Barcode Scanning V. RFID Scanning
RFID
Multiple tags scanned at once
Scans tags even through obstacles
Can be uniquely identified when scanned
Combined with timestamp -
easy to not scan one thing twice
Barcode
Can only scan one item at a time
Needs to be visible to scanner
Identified as a product not indiv.
No use for timestamping
Compact-Disc (CD) &
Digital Versatile Disc (DVD)
Types
CD-R & DVD-R are read only
CD-RW & DVD-RW are read and write
Optical media
Computer Science - A-Level Revision
